To receive spousal support whether your mothers husband is in the US or not there must be a dissolution proceeding. She needs to file for dissolution (divorce). Whether or not he can be compelled to pay depends on a great number of factors not the least of which has to do with is he an American citizen, bank accounts or property here etc. That is too complicated a question to answer in this forum.
To protect her assets your mother should again, file for dissolution. If she won't file for dissolution she should at least file a legal separation so their credit reports wouldn't be intertwined, he couldn't have access to any formerly joint property that she could be awarded by the court etc. could file for dissolution of marriage or at least file for legal separation. Both routes will keep your mother from being liable for any debt her husband may incur after leaving her as well as bar him from accessing her bank account, credit cards etc.
Without a list of her assets or at least the character of the assets, what states they were located in and how they are held I wouldn't be able to give you a more detailed answer.
If your mother needs further help on this issue feel free to have her give me a call or shoot me an email to schedule a consultation.
Good Luck!
Dawn R. VanHorn
Attorney & Counselor at Law
VanHorn Legal
(714) 396-4152
www.VanHornLegal.com
The foregoing has been written by Dawn R. VanHorn, Attorney & Counselor at Law. If the designated recipient(s) of this communication have not fully executed a retainer agreement engaging Dawn R. VanHorn and/or VanHorn Legal relating to the subject(s) of this electronic message nothing herein constitutes nor is intended to be legal advice and as a result should not be relied upon as such.