Even if he has money, she would have to prove in court that it was a loan and not a gift - that it was agreed from the outset that he would repay the money.
Unless she has something in writing then it will be his word against hers.
If she won in court, she may still have a problem enforcing the debt. She may have to get the bailiffs in, or an attachment of earnings...
And she would still be liable to the credit card company - even with a CCJ against the ex, the credit card company will chase her for the money, and she will always be liable.