Advice desperately needed!

My 6 month old refuses to drink in the day. When she was 4 months she was on 6-7oz bottles of formula 4 times a day with 1-2 feeds at night. Gradually she started to drink less and less milk at her feeds she was drinking around 3oz then I had to fight her over about an hour to get the rest in her. So I started giving her little and often and was feeding her nealr every hour. And some she drank and some she didn't. So I made the choice about a week before she was 5 months to introduce food (I was going to wait until 6 months) I just gave her finger bits to taste and porridge in the morning. Then after a week I introduced a tea time meal and she was loving it but her milk intake in the day got less and less and more and more at night. Now shes on 3 meals a day, has 3 good 1hr+ naps a day but doesnt drink a single drink all day. I offer her milk after about 2-3 hours after shes had a meal she has a few sucks of the bottle and refuses the rest either turns her head away and cries or plays with the teat in her mouth. It's like she wants it then realises what shes doing. I offer her water with every meal she has a few mouthfuls. I've tried different bottles, I've tried holding/laying her in different positions I've tried giving her it to hold herself. Nothing is working. At bedtime shes begging for it whilst I'm getting her ready for bed she downs an 8oz bottle and then wakes between 10-11 for a first 5oz bottle, then wakes between 12-2 for another 5oz bottle then wake again between 3-5 for a 3oz bottle and if I didnt offer her another drink that would be her last one till bedtime. She doesnt seem to want a drink her nappies at so much drier than they should be and I'm paranoid about dehydration. I'm keen to cut out her night feeds because they are killing me I'm getting hardly no sleep and my other daughter is having trouble sleeping too so between them both I basically dont sleep. I really want to wean her off then but then what if she still doesnt drink in the day or it doesnt work because she needs them at night due to not having them in the day I've never known a baby like this. I literally have no idea what to do next?