It's fairly creepy, illegal for the moment.
That's end of Uni age dating a year 10/11.
I'm not sure what you can do, as I imagine she would find it rude that you are questioning her if you talk to her about it.
Keep an eye on them and if you find that anything progresses further, immediately talk to her about it.
Talking to her parents if they don't know would be the best choice, but would also end your friendship.
Sorry, this might not help. Good luck.