Can an EX Wife demand and increase on alimony from the EX Hubby even if their son is already 21?

This is in California. My friend got married to this this guy who had his divorce 2 yrs ago. The EX of the guy is so MEAN and my friend is scared that the EX would go to court and ask for more money from my friend's now husband. Does the EX wife have legal rights to get money/increase in alimony from the EX husband even if he is already married to another? They have 1 son - who is now 21... and he is done with the child support. I don't know what to tell my friend, I have not been divorced :-)