I think it depends on the kid, my oldest was completly day trained by 18 months, and most nights, but we did not take away the diapers at night until 2. She wanted to do it, and would tell you when she had to potty, everytime, there was an accident here and there, but not many.
My other two girls were trained at 23 and 25 months (and the 25 month one would of done it earlier, but we had a trip to disney, and I did not want to deal with training there, so the day we got home, the diapers were gone) Both my oldest were night trained at the same time as well.
I personally think you just don't make a big deal out of it, if they go, yah, then if not, so what. But, you have a girl (they train earlier, and easier, most of the time), and I personally don't think it will hurt to get the potty out and see what happens.
Plus it is SUMMER, nothing better than nakie potty training!!
H