If she wanted it to look like a principled choice, she should have done it before it was officially announced (and a done deal in private) or just after it was announced. Waiting until it's in place and public opinion is clear gives the appearance of yet another politician checking which way the political wind is blowing before making a move.

I could see her using this as pressure and a lead up to Trudeau stepping down so she can throw her hat in the ring with a little extra political capital and distance from the ruling cabinet.