Need info on my grand daughter's EOS Rebel T7 lens dimensions

[showme]

My teen granddaughter recently got a Canon EOS T7 Rebel with an EF518 55mm. She's volunteered to be a photographer for the school newspaper, so my wife and I wanted to get her some lens equipment for Christmas. My wife handled the search and purchase of a lens set that she found on amazon that stated they fit the T7, along with a list of others.

It seems that my granddaughter's camera's lens base is smaller than the one's we ordered. They are 58mm, and as far as I can see, when I measured her camera (she didn't have the manual with her, and wasn't sure where to find the base measurement on her camera), I found it is 50-51mm in diameter, depending if I used the inside diameter (50mm) or estimated the thread depth diameter (51-?). So, after doing a little research, I see there are 50mm lenses, but I'm a little mixed up here, since the box that her camera came in states the zoom lens is 55mm(??). 

What does this 55mm dimension indicate, the lens diameter or the base diameter? And, would her camera's lens base be considered 50mm or 55mm? I really can't see another 5mm of thread depth on top of the 50mm inside diameter of the camera's female lens base receptacle. So, as a no-nothing grandfather of a future photography nut, I'm asking all the experts here (i.e., anyone who knows more than me about these things) for help to figure out exactly what we need to get her. Btw, I realize we could wait until Christmas break is over and have her ask her instructor about it, but she was so disappointed when she found out she wouldn't be able to use it this week, I wanted to find one that fits her camera asap. This is what my wife ordered, and is now being returned. Their bases were too big to screw into the camera.

Thanks for any and all comments and suggestions on this. I appreciate it. Lee

[Commercial link removed per community guidelines and replaced with screenshot to serve as a visual aid.]

[shadowsports]

kvbarkley is correct.  The crop factor applies based on the sensor size. The FL does not change.  The OP is using a APS-C sensor, so my previous statement does not apply.  kvbarkley, thanks for pointing his out.    

[Tronhard]

Having read your highlighted response, I thought I would reach out to offer some solutions for learning about cameras and photography - it will help you keep in touch with your granddaughter's progress, and you never know - you might get the bug yourself!
If you go to your local library's on-line catalogue and search for an item called LinkedIn Learning (aka Lynda.com) you will observe it is a electronic resource, or some similar phrase.  It is actually a free gateway into a learning site run by Microsoft that covers a vast array of technical disciplines, amongst which is photography.  By going through the library (if available) you can use the library ID and PIN to access it for free.
If you do gain access, I suggest searching for Photography Foundations, which starts right at the basics and takes you from there.  The video courses are taught by professionals who are also great teachers, and they can be done in sections or repeated at will.  The range of courses goes from basics to advanced topics.

Another resource is on You Tube and is a complete free basics course from National Geographic photographer Chris Bray, an Aussie (so, one of my mates across the 'ditch' from NZ)  here is the link:
Learn Photography - Simple, Practical - Free Photography Course 1/10 - YouTube

I had to smile at your comments about metric.  NZ, moved from Imperial measures to metric in the 1970's, and as an engineer at the time, I was in charge of the transition. Once made, it's much easier to manage measurements with modern calculators and computers than the Imperial system, designed for a non digital-world.  I think there are now only three countries in the world that are not metric: USA, Liberia and Myanmar!  Yet, the US is secretly metric for most of its industrial design and processes, putting it in that challenging spot of being in transition.  I believe that it was proposed some time ago to go metric, but lobbyists in Congress stifled it to avoid costs to business, rather a pity I think.

Now, where I live, there have been generations of people who have known just metric and in a friend's car one of us used the phrase "give them an inch and they'll take a mile".  This elicited an inquiry from his kids as to what that meant.  It doesn't quite have the same impact to convert that: "give them 25.4mm and they'll take 1.6093km"!

[showme]

Finally got her lens in yesterday and then delivered it to Kate. She immediately got out her camera and put it on. She zoomed in on a portrait at the end of the hallway and was really happy with it, although I could tell it will be a learning experience for her. She "kind of" recognized some of the features, but I'm sure she'll need some help learning about it. First of all, thank you all for directing me to the correct lens and away from a mistake for her. Also, for all the information you've given me on this subject. I'm still digesting some of it. 

For Kate's sake, can someone direct me/her to a good learning tutorial or manual that would help a beginner like her. I know she'll get some tips from her instructor, but if she's anything like me, she'll want to research it for herself, also. The lens was brand new in its original packaging, but I guess as is with all professional grade (to me, anyway) equipment, there wasn't any other information in the box. Like a manual for newbies that need some help. Where can she find that information? I'm just starting to look, but I don't want her to be so intimidated that she puts it down and hesitates to use it, so once again, I'm asking all of you. Thanks again for all the help, folks! Lee

[Tronhard]

I would suggest the following learning resources:
For a very basic intro to photography with a dedicated camera, I suggest investing a couple of hours for this free course by National Geographic photographer Chris Bray:

Also, go to your local library on-line catalogue and look for an item called either LinkedIn Learning or Lynda.com.  If it appears in the catalogue, you can use your library card and PIN or PW to access this site free of charge.  It contains all kinds of learning materials on many topics, but there is a great resource for photography.  The courses are presented by professional photographers who are also professional trainers.  They are broken into bite-size chapters that one can repeat as required.
If you don't have access via the library,  you can get a free month by going to LinkedInLearning.com, but the library access is free without limit.
Once on the site, do a search for Photography Foundations and go from there.  There are topics from the basics to advanced techniques and post production.

[showme]

Thank you, Tronhard! That's great, and I will pass this on to Kate. 

[showme]

I found the page from Canon's site that includes the manual on the lens, along with a truck load of other information for her to peruse. What a gold mine of information! I should have looked before I asked, but you all have given such good information, I think this is a great place to start.