In the first two Potter musicals, Hermione was played by Bonnie Grueson.
She was great. She rocked The Coolest Girl and made this cool behind the scenes video of AVPM,
And then she just vanished. OK not really, she has a twitter, so we know she's still alive, but she has never again been in a Starkid production. Not even AVPSY, when literally almost every other actor who'd been in one of their shows came back for. It's kind of a mystery what happened to her and why she left the group. If you start to google her name, "What happened to Bonnie Gruesen?" is like the third search suggestion. The Starkids tends to make jokes or just not reply when asked... It's a mystery. Except somewhere on twitter I read that she was making a movie about Jesus vs. Zombies, so there's that.
Anywho, Meredith took over the role in AVPSY, with a joke about how a spell made her look pretty different.