Colin
She is a lucky girl to have such a supportive partner - but I am sure she knows that already!
I think the joint bank account is a good idea so that you can keep your eye on the joint household spending. I personally would not use my equity to fund someone else's debts if they could afford to repay over a realistic period, but do be aware that she is probably paying high interest rates.
Why not compromise and tell her that you will consider paying off the remainder of her debts when she reduces them by £10,000. Incentive for her to work hard at a reduction programme, and leaves you less exposed to eventual borrowing. Just a thought!
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
For further details contact me at
http://www.melaniegiles.com and view my IVA blog at:
http://melaniegiles.blogs.iva.co.uk