A huge consideration is how much photography she would be doing under lower light settings. Depending upon the high school, lighting in an indoor gym or on an outdoor football/soccer field under the lights can be a big determinant of what is needed for sports.
Going used is the best way to get into the performance needed at a reasonable price point because cameras that do well in low light and lenses designed to let a lot of light through the lens are both expensive. Outdoor baseball in the sunlight is easy for any camera but indoor basketball in the gym or football and soccer after sundown are MUCH more demanding.
Canon has followed Sony and Nikon in replacing their older DSLR bodies (like your daughter's current camera) with MILC (aka mirrorless) cameras and that has resulted in a lot of used very capable DSLR bodies at attractive prices. I think you are much more likely to find something in Canon's 6D2 or similar DSLR line that will also leave enough in your budget to buy a suitable lens so that the combo will handle low light well.
Don't rush into anything and I will do some investigation of what is available and give you some more complete suggestions tomorrow but I just returned home from teaching a MBA strategy course so it has been a LONG day. I have done sports photography for years under a lot of conditions and I will be happy to share what I know. But the most important thing in sports photography is location and the second most important thing is having gear that will handle the lighting conditions that are frequently not so great at the high school level. Daylight sports are easy, when the sun goes down it is a very different situation. The football photos are from a couple of weeks ago on a typically dark high school field and the soccer photo is from the same demanding lighting situation while the baseball photo was an easy shot with the bright sunlight and soccer is also easy when they are played in the daylight. All of these were using high end Canon bodies and lenses but you can still get a lot of good photos at the next level down however once you step down to a lens where the aperture is not suitable for low light action (this is the "f" part of the lens identifier with a lower number being better), then it is no longer going to work well for sports. Another option is potentially making the decision to restrict the type and quality of images your daughter will be able to capture in night/indoor sports but that is a less desirable option in my opinion but it does greatly reduce what is required of the equipment and thus its cost.
Rodger
