I’m so sorry. I am petite with a large bust and it’s really hard when you are little. Even finding clothes can be tough. For the bra, herroom.com has band sizes down to 28 (I just looked), so you can start there. If she’d be a 26D try a 28c. Also try a bunch of brands and sizes. Good bras will cost more. I also remember sewing my bra bands to make them shorter and a seamstress can do this too (meaning any place you go for dry cleaning). Lastly, just a tip - as she gets older when it comes to shopping, it may be better to order a bunch of stuff and return vs trying to find stuff in stores. This is still easier for me and I don’t have all the hang ups of a teen. Good luck!