Gidwick
It sounds like you never actually terminated her employment, is that correct? In which case her resignation stands.
As to the the issue of whether holiday pay is accrued on long-term sick, this thread would suggest NOT, so I suggest you write and decline her request for backdated pay.
http://www.personneltoday.com/discussionforumt hreads/2007/02/28/1/26155_c4a04e79-d4b6-4a50-9 d4f-449b5bda9f71/holiday-pay-whilst-on-long-te rm-sick.html
As far as the retraining goes, the bar work is arguably more manual than a secretarial position which she may say is easier on her back because she does not have to stand as much, reach as much and/or lift as much. I empathise with you feeling she has played teh system but you dont really have anywhere to go with that one. DOnt forget of course that at some point she will want a reference....just bear that in mind.
But PLEASE, get contracts of employment in place for the rest of your staff, the contract protects you alot more than it does your employees. ANd if you stop paying someone or expecting them to turn up for work, send them a letter terminating their employment. This neednt be complicated, you can get a book from WH SMith with personnel proformas in it for contracts, offer letters, termination letters, disciplinary reviews etc etc - you just photocopy and fill in, or amend as you prefer.
Maypole