To all those saying make sure she's only got a debit card now, that's not the answer either.
My mate was exactly like this, he'd spend on loans, cards, whatever as long as he had a way to move the problem on when someone came calling. It all got too much and he just stopped paying. There were no assets there as he'd consolidated all car loans etc into a bank loan so nothing could be repossesed.
Once he got married his wife took all cards off him. It absolutely had to be done. Money was dished out at an agreed rate and anything above and beyond that had to be discussed and agreed. He was removed from all joint cards and bank accounts.
As crazy as this sounds, you're the only one in the relationship who can manage money. You have to make a stand on this one (if you're taking on the debt) and get agreement that the spending stops unless you agree it. It will cause arguments BUT you have to get her on a budget and stick to it or this problem will not end until you've lost her and possibly your house - even if you split she's the mother of your child who I'm sure you won't want to see homeless and up the creek.
If you don't stop her spending it won't stop - about 8 years on my mate has just come out of debt, it was hard on them, but I'm fairly sure he still won't have any kind of free reign on cash.
And sorry to add but make sure you go through everything - if this has just come out it's fairly likely she hasn't told you everything yet...