When you say she eats 4 times a day.... do you mean in total? Just bottles? Or bottles and food?
Ian pretty much eats whenever he's hungry. I do 3 "solids" meals a day, and he gets as many bottles as he seems to need. He usually takes 6-8 ounces at a feeding, and usually has 4-6 bottles a day, and solid food 3 times a day. He's always hungry.
I guess you have to somehow figure out whether or not she's truly hungry by offering her food/bottle more often. Some kids just need to eat more frequently, but smaller portions. Maybe adding another bottle or two during the day would help. I dunno.