Perhaps her move to the LibDems was teenage rebellion against her left wing parents, but the move from there to the Conservatives may have been prompted byTim Farron who was speaking to a group of LibDem students and jokingly remarked that "this would be a good time to be a Tory candidate" because of the poor quality of candidates they had.
I think she probably has no political principles at all, but is just ruthlessly ambitious and interested in self promotion. Apparently, after her disastrous performance in No 10, she tells her friends "well at least I've been PM". In other words she had no real interest in what she could do for the country, only what she could do for herself, just like Johnson.