I'm not an expert but nursed my first until she self-weaned just past 3 yrs and my 2nd is still nursing at 2 yrs. For an expert's opinion ... call Maternal Expressions in Folsom, CA. It's a maternity store and lactation consultant all in one.
My suggestion is to just relax and let that baby nurse whenever and however often she wants. From my experience, your milk will meet her demand ... unless you stress out. She's probably just going through a growth phase which happens every couple of weeks I think. Every couple of weeks, mine would nurse non-stop for a couple days and nights and then go back to normal. She also may be playing with the new foods vs. mom's milk and suddenly needed moms again in force. Or she could be insecure about something ... some new milestone she's achieved recently or a change in her daily ritual or yours ... like a move or going back to work or whatever.
Enjoy it - it's a special bonding time and they will self-wean when they're ready ... it varies but parenting-book-guru Brazelton says if left to themselves, they'll self-wean typically at 2 1/2 to 3 1/2 years of age.
A couple things that are supposed to help boost your milk supply are Mommas Milk Tea (avail at any health food store), beer with hops in it (I think you can get hops in tablets or not in a beer form too but not sure), and I'm sure there's more I'm forgetting ... google it or check out a nursing book on it from your library.
Oh, one more thing. A more accurate way to see how much breastmilk your child is getting is to weigh her before you nurse her and then weigh her again just after nursing her. Our doctor told us that one. Then you can see how much milk (in weight) went into her.