Totally fine! Tracy suggests a 4 hour EASY from around 4 months, some FF babies need to stretch to 3.5 hours for a couple of weeks before that stage but a lot don't and can transition to the 4 hour around 4 months (remember there is a big growth spurt at 4 months).
Be guided by her, if she is draining bottles add another oz into them, if she doesn't appear to be hungry at the 3 hour mark stretch her out a bit to keep her milk intake up.
HTH!
Laura