All babies are different. Some sleep more than others, others happily sleep less. If your baby is happy during the awake hours, then she's fine. If she's grumpy or just seems tired to you, then she needs to sleep. I would venture to guess, however, that she may not have a routine in place where she knows that she is to nap. If you do have a routine, could you list it here? It would give us a better idea of how to help.
As for waking up every 3.5-4 hours, it's definitely possible. Babies have growth spurts all the time and they affect nighttime sleep as well as naps. For her age, this is normal.