Moms what would you do? Help especially from moms who formula feed..?

So I just started watching this 4 1/2month old little girl and her mom said she drinks 4 oz every 4 hours of formula. Well this child crys and crys after everything i do. And ofcourse im a mom of a 6 month old so i KNOW she is hungry so finally i give in at 3 hours and by then she acts like she is starving. I feel so bad this whole formula thing sucks cause its all about schedules. also I think she needs more than 4 oz. I think she is going through a growth spurt. But i dont want to not listen to the mom, should i tell her i think she needs a little more? I mean after she gulps down the milk she crys for more! i give her a pacifier and pat her back and she is fine but i guess im just so used to my baby telling me when she is full. So i dont really know what to do. So basically what im asking is if i feed her every 3 hrs instead of 4 like her mom said do you think that would be fine? And should i mention it to her mom that she might be hungry for more?