Agreed that she should have anticipated. However, ultimately I'd probably put the OP slightly more in the wrong. In a similar situation on, say, a motorway in a car, if a vehicle pulled into the next lane without looking, I think any resulting accident would probably be put upon the vehicle moving out, rather than the vehicle not anticipating that move (even if it was obvious they were about to move out because they had their indicator on for example).
Whether that is a good comparison to this situation or not, I'm not entirely sure. Still, nobody came off at the end of the day. That's what counts. Perhaps next time she'll think to hang back a bit in that situation.