As far as I am aware the holiday entitlement starts immediately, and it is a minimum of 28 days per year. You have no entitlement to take bank holidays off so if you do they count as part of your 28 days.
http://www.direct.gov.uk/en/Employme...ys/DG_10029788
Might be difficult getting paid all the money she is due if she doesn't work her notice period. Assuming she has signed a contract her employer could technically take her to court and claim compensation from her.
