I think that as long as she is gaining weight and has no other medical issues, then she should be able to last 2.5-3 hrs between feeds. You don't have to feed her exactly when she wakes, instead work on resettling her back to sleep until the next feed time. This teaches her that it's not time to wake yet, but it's still nap time. She seems grumpy like she's hungry, I'm sure, but it's probably that she's still tired from not napping long enough.
Have you checked our Naps Forum for help with lengthening her naps?