Depending on how far in arrears she is, you will need to get her out by way of either a S8 or S21 notice. It's pointless asking a letting agent to relet the property until your tenant has gone, unfortunately. If anything, you remarketing the property is only going to make her dig her heels in even more.
Chances are, she will actually WANT you to chuck her out, as the council will then see her as being homeless, and therefore move her up the housing queue. Until then, she effectively has the right to remain in the property, so you need to act now.
If you're interested, my company does fixed fee evictions - PM me if you think this will help you.
Give us your property to let and manage, and we'll give you free management until 2009.
www.nr-associates.com
Manchester City Centre, South Manchester, Wigan, Warrington & St Helens