White matter often increases with age, if her doctor didn't bring it up after she had the scan there was probably nothing to worry about.
If you go to the site below it will give you some more information.
Maybe abscess you should further investigate with a doctor
I can understand your concern. I would certainly ask her doctor, if he/she does not sound concerned, then maybe it is OK, however, they should give you a reasonable reply if you ask, if not, see another one.