Not enough information to say.
How old was the child in question? Could a lock on the door been sufficient? Is the kid even old enough to grasp a boundary concept? If the kid is 2 years old, probably not.
It was only for two weeks which means the parents were likely under time stress to make other arrangements. Was the kid being watched by an older kid rather than the parents at the time of the incident? She did say she had to call them all back to the house to tell them to leave.
Was the roommate insisting they be asked to leave or would the roommate have been okay with some sort of amends and conciliation?
I'm not saying her choice to send them packing was wrong. I'm just saying that there's not enough information here to say whether it was the best decision or if there could have been a working solution that wouldn't have caused more chaos to a family she agreed to help. Could they have gotten through the two weeks by conciliation and amends without pulling the rug out from under them again?