Mental block, closely related to (arguably the same thing as) the twisties.
Some kids get over them, some don't. The most important thing -- and this is much easier said than done -- is to not stress about it. For both her and you.
There is a part of the brain sometimes called the "reptile brain," so-called because it's basically the same in structure and function in us as it is in reptiles, and it's the part of the brain that deals with survival situations. Basically, it's the part of the brain whose job is to keep our cave-dwelling ancestors from being eaten by lions, tigers, and bears.
When a bear wanders into your cave, you don't really have time to think how it got there, or why, or what it might want to do; you can figure all that stuff out later, but right now you either fight, run, or get eaten.
A mental block happens when, for whatever reason, the reptile brain has identified some particular skill or category of skills (and backwards-rotating skills are a REALLY common one) as a survival threat. Now, the rest of the brain may know perfectly well that we've done this skill a thousand times, that we did all the necessary progressions, that we did it last week and we were just fine, and that logically there's nothing to be afraid of; however, reptile brain doesn't deal in logic, it only knows two things: fight or flight.
Unfortunately, getting upset about this disconnect just reinforces that the skill in question is indeed threatening. Why would we be so upset and frustrated and angry about it if it wasn't a threat? So we struggle with the skill because it feels like a threat, we get frustrated because we're struggling, and the skill now feels more threatening because we're so frustrated with it. And round and round we go.
I have a few ideas about how I might go about addressing this as a coach -- it would vary a lot depending on the athlete -- but the general idea is to isolate the threat in a way that is as non-threatening as possible. Can she do a backward roll? If not, can she do a roll to candlestick? If not, can she fall to flatback on a squishy mat? Or if she can do a backward roll, can she do a backward roll off the edge of a mat into a pit? A back drop pullover on trampoline? Etc, etc; there's no easy formula.
As a parent, though, it is absolutely imperative that you NOT make a big deal of this. Don't let her see your frustration, don't push her to talk about it unless she wants to, etc. She needs to know that whether she succeeds or fails, she is still safe and still supported. THis is the best thing you can do to make these skills less threatening -- the rest is up to the coaches.
(I will say, though, that this is one of the few situations where I do think a few private lessons would be a good idea)
