I would feel fine if her Mum's at home next door. I am a little biased as I have seen 2 incidents in a hospital setting where a teenager was sitting & didn't have first aid experience in a choking incident. Also in Qld it is not considered okay until the child is 16 years old - I know this as a friend of mine was leaving her younger children with her teen whilst she worked and this was not legally allowed.

Having Mum next door though would be fine for me.