Mother-in-law declining quickly. Could there be other things going on?

My mother in law is in her mid 60's and had two strokes. There was some cognitive damage evident but now the decline in the vascular dementia is very rapid. Two months ago she was holding down a job, now she can't even remember where she is or who people are. Even three weeks ago she was much better. It's been my impression that usually dementia has a slower progression than this. Could there be other things going on? Low sodium levels? Reactions to meds, wrong kids of med, etc? It's very disturbing and somewhat at odds with the many people I have known with age-onset dementia. Any thoughts are much appreciated. Thanks