It's entirely possible that she needs a different med. Actual dosage and the time before a new drug is needed vary wildly from person to person. Don't stress about how long it's been since you started the current med or even what the dosage is. It's more important to know that the medicine is working and that the side effects are controlled. You should be able to tell if a dosage is too high based on the side effects.
Call her doctor and go over the situation. It's not out of line to ask for a change if the current drug isn't helping.