Unfortunately if you have a joint account she will be liable for half of the overdraft and will have to pay some towards it.
Her credit record will also be tarnished.
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk
As Kallis as indication she will be liable, but for all the overdraft - minus and IVA payments made into it.
And because you have joint liabilities - you may find her credit report is damaged