Help - 2.6 year-old holding on for hours

[Impala]

Apologies for the mammoth post!
DD is 2.6 and we started potty training a month or so ago at her instigation as she decided she wanted to wear proper pants. It was a bit hit and miss to be honest and after about 3 days I ended up putting her in pull-ups because she would sit on the toilet (she won't use a potty) not do anything and then wet herself a few minutes later. I explained to her that she could still pull the pull-up down and sit on the toilet (she can pull her leggings and pants/pull-ups down without any problems). At that point she also started to refuse to sit on the toilet altogether so I backed off completely and let her do her own thing. She was weeing and pooing in the pull-ups and then coming to tell me afterwards and asking to be changed. She was dry for several hours in between so I could see that she was starting to get good bladder control. She then started telling me she needed to go before actually doing so but refused to sit on the toilet if I suggested it, so again I just let her do her own thing, occasionally suggesting she use the toilet. She never did a poo on the toilet during that time, always in her nappy in the mornings.
A week ago we decided to try again (again at her instigation) and the first couple of days were fine, she weed on the toilet a few times and had a couple of accidents as expected, but seemed quite happy. However, she's started to hold on for hours (6 hours plus) as if to avoid going to the toilet and then wetting herself when she can't hold on any longer. I started to get concerned about the fact that she was only weeing 2 or 3 times a day and I put her back in pull-ups over the weekend. However, she continued to hold on so yesterday we tried pants again. She's totally dry at night, she goes 14 hours plus without a wee now.
When asked if she needs the toilet she invariably says no, even though it's quite clear she does (she's clutching herself). She'll happily sit on the toilet if I suggest reading a book but then won't do anything. Yesterday and today she did go and sit on the toilet at about 5pm at her own instigation, having not gone for a wee for over 6 hours and then had a wee or tried to so I know she can do it. She goes to nursery one day a week and her key worker says that she's quite happy to sit on the potty at the set times they have (she won't use the toilet there for some reason) and either do a wee or not. I'm wondering if it's a control thing, or if she can't relax enough to allow her bladder to open or if she's scared in some way. It does concern me that she's holding on for so long though. I suffered from repeated UTIs as a child and I really don't want her to go through the same pain as I did. She probably doesn't drink as much as she should, but I can only encourage rather than force her. She eats plenty of fruit so is getting fluids that way too.
I really don't know what to do to help her, I tried to initiate a reward chart but she's either not grasped the concept or doesn't really care whether she gets a sticker or not. I don't know whether to put her back in nappies, which will be difficult as she's refusing to wear them, or to keep going and hope for a breakthrough of some sort. I can feel myself getting really frustrated, although I'm trying very hard not to let DD feel this. Any ideas or help really appreciated.

[girlywhirly]

How fond is DD of her dollies and teddies? What about getting a dolls potty and engaging in a little play, where dolly or teddy sit on the potty and are praised for doing a wee/poo. Or have dolly/teddy sit on the toy potty while DD is sitting on hers. Say that you wonder who will be first to do their wee (you could add an incentive such as a choc button, and unless you have a drink and wet doll it will be DD who wins!) Maybe that would work too, a drink and wet doll, so that there is actually something in the potty to see.

I think it would be good to have set potty times like nursery, so that you are all doing the same regime, when DD is confident in her potty use you can ease off and let her go when she chooses to.

[Impala]

Thank you so much for your tips Girlywhirly. DD has a favourite Minnie Mouse and we've been sitting her on a toy potty for a while now and we've now started a sticker chart for Minnie as well and DD is very keen to give the toy stickers but still refuses to sit on the toilet herself! This morning we even started sticker charts for DH and me and although she was delighted to give us stickers she refused to sit on the toilet and promptly wet herself a few minutes later. We've been playing at sitting toys on the potty for weeks now and read several books where the characters are learning to use the potty, which I think is what prompted her initial desire to learn, but she seems to have totally lost interest. This morning she wasn't even particularly bothered about wetting herself, usually she whinges a bit. She's at nursery today and they will continue the sticker chart with her. Hopefully a bit of peer pressure will do the trick! I'll then continue when she comes home this afternoon because I think you're right, we need to stick to set potty times. Even if she doesn't do anything, I'd like her to get used to going regularly. I'll also investigate drink and wet dolls. Thank you again