Wow, that's pretty severe. My horse is parrot mouthed, but not nearly that bad. It might just be the way you're holding her, but it looks like her top teeth don't touch her bottom teeth at all. If that's the case, she's going to have very hard time chewing food. Your best off feeding her things in very small pieces and soaking it to minimize the chances of a choke.
As for what can be done, your best hope is if the reason for her overbite is related to some uneven growth elsewhere in her mouth. Sometimes the back teeth develop hooks or grow unevenly in height and create an effect where the bottom jaw cannot move freely back to front. This keeps the bottom jaw from coming forward enough to meet up with the top. Once the teeth are filed down by a good dentist, the jaw can move more freely.
I wish I had pics of Puck's mouth to show you. When we first started working on him as a 4 year old, (apparently race horses never get their teeth looked at since he was a mess), his top and bottom teeth didn't meet up either. After a lot of work, they overlap enough to where he can eat reasonably enough, although he's a very slow eater and usually drops more than he chews.
At least she's a baby. I'm sure more can be done with her than with an older horse. My best advice is to find a dentist who is very experienced in problem teeth. Good luck.
You just have to see your distance...you don't have to like it.