I used to be one of those lovely people that calls up people who owe the bank money and tries to make them pay :-)
If debts are in both names I think there's not much you can do about it as the bank (or whoever you owe) can pursue you both and if you are dealing with a mortgage you certainly don't want to default.
If you need the money sooner in the month than she is willing to pay it may be worth seeing a solicitor yourself who will contact her or her solicitor on your behalf.