My mother was granted guardian of my aunt, she needs 15,000 to be bonded and she does not have it. What can she do?

I am a California attorney so my answer may not be applicable but out here the surety (the bond company) will often accept a co-indemnitor (or co-signor) and in some cases even the attorney can be that person (if they will sign). I would ask the surety company representative for all options to get the bond issued.  Good luck to you.  -John