1. If she hasn't already done it, she must make sure the joint bank account is closed. Otherwise he could run up another overdraft on it. If the bank refuses to close it without his signature (& he refuses to sign) she must put the bank on notice in writing that she will not be using the account herself and will not be responsible for any future overdraft. Send it recorded delivery and keep a copy.
2. Can she afford the payments on the mortgage and car? If not, she needs some professional money advice from a free service such as CCCS or local CAB. Do not go to any of the outfits that charge a fee.
3. If possible, the property should be sold. If there is any equity a split of it should be agreed with the ex-partner (may be difficult to do) but it should take into account the mortgage payments he should have made and hasn't.
4. If there is no equity in the property the mortgage lender will probably not agree to a sale. If the mortgage then stays in arrears it will almost certainly be repossessed. If there is then a shortfall (i.e. what the lender gets for the property is less than the amount due on the mortgage and charges etc.) then both your daughter & her ex are liable for the full amount. The lender can chase either (or both) of them.
5. Bankruptcy might be one solution eventually - depending on her overall financial position - but it is not inevitable and may well not be her best option. If she does go bankrupt her liability for any shortfall on the mortgage would be written off in the bankruptcy, as would any outstanding debt on the car loan and any other debts she has.