I would just add that if you find one you/she likes, definitely give it a good “jump test” and also watch on video (if possible) before buying duplicates.
A lot of the stretchier sports bras minimize impact by supporting while also having a substantial amount of “give” to accommodate breast tissue. But you often see people running in these kind of bras and there is a lot of movement happening, even if it is comfortable for the wearer. A more rigid bra will minimize this if fit well, but some women don’t like the more constricting feel and/or they may have rubs from rigid straps.
For something like riding - you might still prefer the look to the overall comfort for things like shows. I use the same example for people who are showing their dogs - even if their bras feel comfortable, a bouncing bosom takes the judges eye away from the dog.
When you’re wearing the bra it’s hard to know what it looks like, so it’s worth having a very honest shopping buddy, good mirror or video.