Personally, I like Shiho. What she went through with violin is a very real issue. If you've built your entire identity around being good or "the best" at something, it can be incredibly jarring and demotivating to see that maybe you aren't all that. It actually happens a lot in the scene of classical music, musicians will get so much anxiety from just seeing their instruments that they have to stop.
I don't think any of this excuses her behavior, but it does explain it, and I can sympathize with her.
Also, this clearly isn't the only reason she left SS Girls, I'm not sure why some people are treating it like that.