"I'm having a bit of an issue with my 15 month old's weaning and fluid intake. She received all of her fluid intake from breastfeeding for the first 12 months. I started to introduce milk shortly thereafter. Prior to the introduction of milk, she would normally nurse 4 times a day (as well as eat 3 meals a day and snacks). I first replaced one feeding in the afternoon with milk and it seemed to be going well. She would drink quite a few ounces of milk from a sippy cup. I then stopped the second feeding and she refused to drink milk as a replacement, but also didn't want to nurse. I have recently stopped another feeding and she will again not take milk as a replacement. At this point she is barely drinking a few ounces of milk from a cup throughout the day and only nurses in the morning when she wakes up. She eats a lot of fruits (which I know have a high water content) but I am very concerned that she is not drinking enough. She still has wet diapers throughout the day, although not the volume she used to have. Also, I have tried various cups and the one we are using is the one she likes the best so I don't think that's the issue. I have also tried to get her to drink water or juice, but that doesn't work either. Can it be that she is getting most of her fluid intake from the one nursing session and fruit??
I am planning to ask the doctor at her 15 month check up next week, but would really like your advice as well."
It doesn't sound to me like she's getting enough liquids. People can go for years with inadequate fluid intake (Exhibit A being my father), so it's not the kind of thing that will stop her in her tracks, although it will make her feel bad. Fatigue, crankiness, weight gain (in adults--I don't know about kids), constipation, dehydration, and odd sleep* are all symptoms of inadequate fluid intake.
She may start drinking more when it gets hotter (I'm assuming you're in the northern hemisphere, so if you're not, ignore what I just said). You could also try to get her to drink more by offering popsicles (you can make them by mixing water and juice and freezing them in popsicle molds or little paper cups with wooden popsicle sticks for handles) or trying different kinds of "milks" like rice milk or oat milk. I could never stand cow's milk--it just tasted/tastes strange to me--but I think both rice milk and oat milk are delicious. Maybe she just doesn't like the taste of the cow's milk, but would go for other milk-like liquids.
She's at the beginning of the testing age, so she may be trying to exert control by refusing something she knows you want her to drink. If that's the case, then the surest way to get her to drink it is to pretend you don't care. Or to pretend she's not allowed to have it. You could take big, drawn-out sips of the rice milk and talk about how someday when she's a big girl she'll be able to drink rice milk, too. It might even work.
I think this is probably just one blip in the process of weaning, and that it'll resolve itself as she figures out the balance of how much she nurses and how many other fluids she drinks. But I'd keep trying (without letting her know you're trying, of course) to see if she'll drink other liquids, just on principle.
Let me know what your doctor says about this, too. I'd be curious to see if s/he agrees and has any suggestions.
* Being tired all the time and unable to wake yourself up easily, but also not getting solid restful sleep.