Small question, big answers! You need to give a more specific example.
In short: any obligation you incur with a bank, credit card co, loan, etc, is yours. If you take it out in joint names, its joint. If in her name, hers.
Being married does not make you liable to lenders etc for each other's debts unless they were taken out jointly.
If one of you is so in debt that they are made bankrupt, the other one doesn't have to pay their debts. You are individuals: the old law about spouses being responsible for the other's finances went out a LONG time ago.
BUT if you get divorced, a divorce court may take each other's debts into account in deciding how to split up the money. For example, if you took out a £5,000 loan for double glazing on the jointly owned house, the court would probably treat it as a joint debt even tho it is in your name.
If you'd taken a loan to pay for an expensive holiday for yourself alone, they'd probably treat it as your debt.