To the OP - I am sorry your daughter is dealing with this. With all due respect to those that tell you undoubtedly she will get the skill back or that it will for sure get better, I am sorry - but no, that is not always the case. There is a lot of great advice already posted to this thread--
@NutterButter provided some great insight.
My DD has struggled with backwards fears starting about 2 - 3years ago ( I am starting to lose track of time). She is/was a talented gymnast. Always had great form and strong skills - she was a kid that stood out. However, seemingly out of nowhere she began to struggle with her RO-BHS. We did everything 'by the book' and some days were good and others were really bad. Her backwards fears spilled over to her BWO on beam, and eventually interfered with her giants on bars - they also started to interfere with her flipping vaults. My DD worked, and worked, and worked at dealing with these fears/blocks whatever you want to call them. She would do them perfectly one attempt, and the next time would be gone. Last season and the season prior, she competed well all season, but right before states things fell apart yet again. Even with cobbled up routines last year as a 10 year old Level 7, she qualified for regionals and placed there with the same cobbled up routines. She worked all summer - frustration, frustration, small success, frustration. My daughter competed one early season meet this year as a level 8 and then made a decision I truly never thought she would. She decided to walk away from the sport. She had grown tired of the constant battle between her body and her mind. She was exhausted and wanted so badly to experience success again.
I don't tell you this to scare you.... I hope your daughter is able to overcome this block in its entirety and work through it. This could be her simply growing and she will readjust well. But my DD's tale is one of gentle caution... we were on a rollercoaster ride of emotions with my daughter after doing everything 'right' and then again struggling one year later. These things take time, and for some, like my daughter, they are never able to overcome them. Things can go well for awhile and then boom - back to square one. I am so proud of the efforts that my daughter made time and time again and I truly don't feel like she gave up; it's just that there comes a point when you know you have battled enough.
I will add - that a good coach will pull the skill if there is concern for balking. It's unsafe and when you have a kid who is clearly a thinker - overthinking in this sport is problematic - and those who are not consistently throwing a skill should not be doing it at a meet. I would have a chat with the coach to see where things are at. Good luck to you and your DD!! Keep us posted as to how things are progressing for her!