Well it seems apparent that someone is forcing her to do those stuffs and perhaps her scuffle with him ended up being her breaking point, or perhaps since the schemes has all been blocked, the person forcing to do those stuff decided to do something drastic and she ended up doing...well, that, because she can't handle it anymore.
Someone from the management or someone she knows in the past is a good bet. The idol girl from last time is very unlikely though, disregarding how Miya act towards her in Charisma mode , the girl looked way too intimidated by her to be the one forcing her to do criminal acts.