Its past time in my opinion. They should have there 1st check up rather early. Best get them used to the dentist and make sure theres no problems. Baby teeth make way for permanent teeth. And often baby teeth are prone to getting cavities.
I took my son when he turned 2 which is the recommended age for them to have their first dentist appointment. I'm glad I did too cause even though I took immense care of his teeth, it turned out that he has soft enamel which meant he is very prone to cavities etc and ended up having to get surgery performed on his teeth such as cappings and fillings.
We always reccomend sending them rather early. When they have a few teeth in there mouth, bring them for there first visit and have them watch you and big sister or big brother getting there teeth cleaned to show that it is not a big deal. And at your next appt. make an appt. for her as well and everyone can have there teeth cleaned at the same time.