How to encourage uninterested toddler in pt!

My daughter is 2yrs 9mths now and still very firmly in nappies - whilst I'm not bothered in principle, in practice her cloth nappies really don't fit very well any more, if at all - we have just a handful that are still reliable, and the rest leak or have to be changed after an hour, or just plain don't fit! (I can't afford to buy a load more either, at this stage)
We started practicing with the potty a long time back - say, 5mths now - and she was very excited to begin with, but then the novelty wore off. She doesn't often have dry nappies (ie. doesn't hold her wee), altho sometimes she does, so she is capable physically......she used to have dry nappies more often last year, but hasn't for several months now. She will either not be remotely interested in sitting on the potty (definite "NO") or will sit, but then doesn't need/know how to go but will remain adamant that she's going to stay there until she does something...which can, and has, taken up to an hour - not at all practical!
I work 3 days a week, taking care of other children in addition to my daughter (ie. I'm a nanny) - including 2 days per week when I have 3 children under the age of 3 in the house. So simply putting her into knickers to see if a few accidents will prompt her further isn't really practical either - it's hard enough to get us all out of the house and/or enjoy our activities together when things are running smoothly!!
I feel as if I'm being a bit lazy in not just trying knickers - she likes the idea of them. But she doesn't seem to have much clue of when she's weeing, or predicting when it's about to happen, neither actively having much bladder control to hold it. Interestingly, she does a lot better on my work days, as one of the other children is potty trained and she will imitate her, sitting alongside her on the potty and weeing almost every time.....but then refusing to do so on days at home when it's just me and her!!
AArrgghhh!! Any advice appreciated!!

I would persevere with the knickers. It will be hard at first but she will get the hang of it. I think you need to be fully committed to the idea though otherwise she'll pick up on that and stop trying. Both of mine liked a sticker chart which we did for a week and then stopped because I wanted weeing in the loo to become the norm and not something that needed rewarding as such.

Have you tried her on the loo rather than a potty? Again, neither of mine liked the potty and used the loo straight away, mimicking us I guess.

It mightn't be what you want to hear, but I wouldn't persevere. If she's not interested and doesn't have the bladder control you're only making work for yourself. I would wait until she wants to do it, that way (hopefully) it'll all be over in a matter of days when you do go for it.
Could you maybe sell some smaller nappies to fund bigger ones, or maybe try freecycle, I know people who've got entire stashes through there.

Do you have any time off coming up where you could let her run round bare bummed for a couple of days

No suggestions but Nathan is still like this at 3 years 9 months!

I agree with Caroline and smj, sounds like she coold do it, but needs the opportunity to learn bladder control, and how to hold it before going. Its a whole new physical process so will rake some time x