I think she's potty trained at a really bad time. Surely there's a week where Ivy is with her dad during the holidays? She could have potty trained then so both kids weren't house bound. Has she not arranged any play dates for Ivy, so Ivy could have gone out?!
Also, when she was working part time and home with Mase a lot (before he started nursery) she could have dedicated a lot of time to it then, as they didn't use any childcare, it was just her and Rob looking after Mason. Once you start chucking in childcare etc, if makes it a lot harder.