how do i figure out what size bike to get dd1?

[misdee]

inside leg is 17inches. how do i know which one to get?

Misdee I really think you need to try her on one if poss. We got a much bigger bike for DS1 than I expected.
Failing that (ie if it's a surprise) a good bike shop should be able to help you, and change it if it's not right.

I would guess a 16 or 18 inch one, as she needs to be able to touch the ground when she is sitting on the seat. A 14 inch one woudl be too small i think. What about something like this

Girls bike

Best to try some. Even if they are the same frame size they do not feel the same to ride (for e.g. because of differing length of the bit of metal the pedals are on IYSWIM).