Is she having breast milk in her bottles? If so it's not really unusual to be honest - many breastfed babies can't go 4 hours between feeds at this age because breast milk is digest far more quickly than formula.
I would increase her bottles to 5oz of you can and keep her on a 3 hourly feeds and see if that helps. As Erin said, there is a big growth spurt at 4 months and that could be causing it too.
She probably needs more than 24oz in a day too. How much does she weigh? A rough guide for formula is 2-2.5oz per lb of body weight in 24 hours, I'm not sure if that's the same for breast milk but if she isn't satisfied at the end of a bottle it does sound as if she needs more.
Laura