My DD had fears of going backwards on beam. She struggled for months with the BHS. I didn’t ask her about it much, but just encouraged her when it did come up. I think it helps to know too that your DD isn’t the only one that has ever experienced a mental block. Knowing that other gymnasts dealt with it too helped her to not feel so alone in the struggle.
Another thing that really helped was a four part series by Doc Ali on getting over mental blocks. It’s on YouTube I believe. It gave my daughter some practical advice and helped her build progressions. I think it helped her feel like she was making progress even if she hadn’t yet done the actual skill on her own. If gave her tools to help reset and a place to start over instead of just standing on a beam waiting to get over the fear.