L.H.
You're not paying her to socialize. I'd let her know that its totally okay to do once the kids are asleep but that while they are up and awake, you'd prefer that she played with them, helped clean up and got them supper/baths and in bed on time.
I was a nanny for a long time and when the kids went to sleep I picked up the rooms we had been in, wiped down the counters and read a book or magazine I had brought with me. I don't think its too much to ask as long as she's paid pretty well. I mean - I could make $50+ in one night, the least I could do was pick up some toys and keep the dishes from piling up.
Just my two cents!