you might find that she doesn't drink much of either, I found that our LO would only take a sip or two as I started weaning, so quickly was only on one feed a day. It took a good four weeks to build up to drinking 100ml at a time.He is 2 years old and even now, hardly drnks fmore than 50-100ML a time, he sips his drinks in little amounts throughout the day.
He was never on a bottle either and took well to a sippy quite young like your LO. I just found that he preferred water, he didn't drink much of that either. I got advice to mix some formula/milk into a bananna smoothy if I was worried. I guess you just got to look at their overall calcium and iron intake, and make sure that it's ok. There are plenty other ways to get those nutrients other than milk, and other sources are better absrobed by the body, like fish with bones. That's what I ended up doing, we focusing on getting 3/4 cup of yoghurt, some tasty cheese daily, offeering fish at least 3 nights a week and red meat the others, spinach with lemon juice a few times a week and fortified rice milk for drinking.
Anyway, hope that you LO just loves the milk / formula and you don't have to worry!
I hope that your supply is ok, mine has always been abundant and I struggled with lumps alot, but funnily enough weaning gave me no trouble. I am thinking that the LO's take in so much less as they have been on solids a long time anyway, so engorgement is not such an issue.