2 year old girl who won't eat

It could be a lot of things. Sometimes it's just a phase (you didn't indicate how long this has been going on, or whether she's actually lost weight since she stopped eating), sometimes it's just the normal terrible-twos rebellion, and sometimes there is a medical reason for this.

We've had to deal with the first two of those situations, and have a nephew that has a medical problem with food.

In each case we tried several things:

• Feed them what they are willing/able to eat. If that's just 8 glasses of milk a day, some fruit snacks, and cheese, then that's what they had because they were willing to do so - as long as they also took vitamins. We had one 18 month old that wasn't eating enough 'regular' foods and had already weaned himself. The doctor had us feed him whole milk all day long. We offered other foods to him as well, but the doctor indicated that whole milk had enough nutrition and calories that we needn't worry about feeding him other foods if he wasn't interested. That went on for several months before he really started eating more regular food than milk. Check with your doctor, but some one or two food diets are sufficient, and can get you past some stages of food problems.
• Feed them on-demand. While it's convenient for us to be on a schedule, we were advised that for one of our kids that we should be paying attention to when they felt hungry, and satisfying it on demand. It seemed that part of the problem with one kid was he didn't associate the feeling of hunger and food. When he got grumpy we had to get him to eat a little, and eventually he recognized that he was hungry at dinner, rather than just grumpy and uncooperative.
• Give them a choice. We tend to try to prepare only enough for the meal at hand, so you either like it, or you don't, but you don't have choices. This created a lot of friction, especially for independent minded toddlers. We've learned to provide several choices at most meals (while occasionally limiting it so they do have to get used to the sometimes-I-have-no-choice situations) and this give them a sense of control over what they eat. Mostly this is a "We can make you x, y, or z if you don't like what's on the table" but even if we prepare other foods in advance they are stored and used later so there's not much more waste.
• Teach them about the consequences. At 2 this is hard, though, but if the above wasn't working I suspect we'd still go ahead and explain during dinner that if they didn't eat they would be hungry later, and later they might not a get a choice as to what they will eat.
• We did have a few instances where we had to pull out the, "You can feed yourself like a big boy, or we can feed you like a baby. Your choice, but if you don't start eating now, then when I'm done I'm going to start feeding you." I think once or twice we even had one of them sit at the table in front of their uneaten (or slowly eaten) food until bedtime when they fought being fed.
• We don't want them to be afraid of going to the doctor, so we never said this, but I think telling them that if they don't eat enough they'll have to go to the doctors to see why they aren't eating would work particularly well for some children.

We did have short phases where a kid would seemingly not eat for several days at a time - several bites at each meal, but these lasted for only a few to perhaps several days, and then they've be back to their normal self.

The above will really only help when it's a issue of motivation or independence.

It's important that you don't ignore the possibility that there's a medical problem. Keep track of your child's physical activity, weight, and intake. If they aren't consistently gaining weight, or if they are lethargic or sleepy most of the day, or seem to have frequent bouts of illness, consult with your physician about their diet and share your tracking information. 25th percentile isn't bad, and is generally well above the line needed to be diagnosed as Failure to Thrive, and due to the curve on the weight chart there's a big difference between 1% and 25%.

If your child is otherwise happy, active, and gaining weight, then they may well be eating what they need.