How to Get Out Out of a Expensive Mortgage?

refinanced

Is there any excellent way to get out of an upside down mortgage? My ex wife currently owns a house that she really can’t meet the deprivation of. We refinanced the mortgage when we got diovrced 5 years ago. Since then, she has refinanced once more. With the current housing market where she lives, she owes more than she could get for it by selling at a reasonable price. Does she have any options to get out of the mortgage?
If my ex wife sells the house for less than she owes on the mortgage, and owes the difference to the bank, is that money owed at the time of closing or is it paid back as a personal loan?
I did try to help her sell it when we got divorced, knowing it was too expensive for her to maintain with her financial situation. My advice was not well received, as she wanted the status symbol of a huge home. I no longer have any financial obligation on the home, so it is not my problem to resolve.
For anyone who wants to know my motive, there is no motive for me one way or the other. I don’t subsidy one way or the other. I do care about my children though who live with my ex wife, and building sure they are cared for and have a nice, reasonable place to live. I pay my child support and she needs to also be able to adequately take care of them and share the costs of raising them.