There is a later lens in that model, the Canon EF-S 55-250mm f/4-5.6 IS STM unit, which is an improvement, but the one you quote is quite a good unit too (I owned one). The STM version has dropped the price on the one you mention.
I would recommend looking at sites like DPREVIEW.COM to see what lenses Canon has made and see some of the reviews. Just avoid the tech trolls!
The following images were made with a 10 year old Canon 400D (10 Y.O. body) using a 15-85mm stitched together. NOTE the resolution had been reduced to make posting easier, still I think it reinforces my point.
The T6 would be good, as well as an SL2. One thing she will really like is that the SLR's will have much more responsive shutters.
The 55-300 will be good for wildlife, but at some point you might want to add the "kit" 18-55 for wider-angle general purpose and the 60mm macro for those butterfly shots:
One important question for her is what she wants to do with the photos she takes. Is she going to show them on a web page, look at them on a monitor or print the images. If she is going to print the images how big does she want those images to be?
The reason I ask is that output has a big impact on the kinds of gear one is going to use. The requirements for output to screen or small prints do not necessarily require expensive gear. If her needs are not IMMEDIATELY demanding - she is after all at the start of a learning curve, I would recommend getting a bridge camera. A bridge camera has the same basic controls of a DSLR, but is a lot smaller and has a non interchangeable lens. What it does have is a lens with an amazing range: from very wide angle to super telephotos.
I am going to use a term called equivalence here. It is simply a means to compare lens performance from different type of camera on a standard scale. The numbers written on a lens are relative to what that lens would see (called the Field of View - FoV) on a full-size sensor (a sensor the size of 35mm film), a Canon T6 has a smaller (crop) sensor, so a lens on such sensor has its FoV focal values multipled by the crop factor (in this case 1.6) to get its true FoV.
For example, the lens you were talking about on the T6 has what is called an equivalent range of 88 - 420mm (1.6x 55 to 1.6x 300), while a bridge camera such as the Canon SX60HS has an equivalent range of 21 - 1365mm! That's means the lens can 'see" a much wider range!
A bridge camera is more compact and lighter, so it is easier to carry (as the saying goes the best camera is the one you actually carry). It has a smaller sensor (think smaller negative if you like) so images cannot be blown up to as big a size as those from larger sensors on more expensive cameras. That said, the images one can get from a bridge camera can be very good. As below.
The image above was taken with the Canon Powershot SX60HS bridge camera,
This image was taken with a Canon 7DMkII, with a 100-400 MKII L lens, and 1.4x MkIII extender
This is Professional level camera system that cost 10x the amount of the Canon Powershot SX60HS. Can you see 10x the difference in these images? On a screen or small print (8" x 10") I would doubt that too.
So I would submit that the bridge camera is perfectly capable of deliverying excellent results for a very reasonable price - they are available for less than $500US. If you were sticking to your budget you could then consider a tripod and a cable release to help your daughter with the types of images she wants.
"Better equipment does not make you a better photographer,..."
However, you don't see most pro's using cheap gear. 
Wonder why?
@ebiggs1 wrote:"Better equipment does not make you a better photographer,..."
However, you don't see most pro's using cheap gear.
Better equipment will make any photographer better. How much better depends on how good you already are. The better you already are, the more difference better equipment makes.
