hello, and I think yes you should talk to her mother, about what she did, she is curious about puberty, and she is easily pursuaded with what her friends are doing.but most of all that is not normal behavior for any child at that age...and I wouldnt let her watch my kids. until she has been evaluated...sorry..thing like this should be looked at..talk to her mother..
If she had done this with someone her own age, I would say it's pretty normal, there is even a joke in "A Chorus Line" about practicing kissing with your best friend "so you would know how with a boy." But the fact that she more or less inflicted it on a 1-year-old is something a little different. I'd be sure she knows that kind of thing is not for one person to do "to" another, but only when two people who are equal in strength and intentions agree. It kind of sounds like she's feeling a bit lost and left out of things as well as stressed over the divorce, and wants to assert herself in some way. Ask her more about her life, not as a result of this confidence (so she feels like you're snooping) but because you want to know about it, and just kind of keep your antennae up for any acting-out against someone weaker than herself.