same thing happened to elphaba's mum a while back..
http://www.tfproject.org/tfp/showthread.php?t=89588
it sucks... the situation sucks... your mom will heal and it's only a few pounds...
i doubt the police will be able to do much - but you can help her out... spend time with her- and go with her for a while when she needs to run errands... so she's not alone...
Self defence classes I would also recommend, not to turn mom into a ninja warrior but those classes will often teach a person to be aware of their environment and give them a little confidence when they are alone... a person who is aware is less likely to get mugged than the person who's just not paying attention..