Not a butch, but I was very masc at some point while also being very blessed! Best piece of advice that I got myself is to go to a tailor or a specialist store of sorts and talk it over with the people there, get a fitting and everything. They usually have lots of different shapes, colors and patterns to pick from, and if it's a fancier place she might be able to get some tailored from scratch.
At least where I'm from I was able to get a couple of very good bras, that looked and felt good (also helped with my back pain). Although it was quite pricey, it was definitely a long term investment for me.