From what you say it is hard to tell. Usually there is some evidence of chocking, even if it is only minor chocking such as a cough when she is eating, if she is having swallowing difficulties. But then she could have aspirated food in a single incident. Is it possible to have a portable chest X-ray done in the facility. That may answer questions. It is probably a good idea to also have her checked for swallowing difficulties. Until you get the therapist report it is difficult to tell what is going on.
My Dad had vascular dementia. He was in AL with Mom who has Alzheimer's for about 18 months before they both had to be transferred to a locked dementia unit. They were both a flight risk! Dad was there a year before he died March, 2010. I never noticed any problems with his eating at all.... yet he lost weight rapidly. He went from 186 to 130 pounds that year.... despite the fact he ate and ate well. He ate scrambled eggs and grits on Tuesday morning before he died on Friday. When he started that final decline it was very quick... just a matter of days.
I do know that Vascular Dementia symptoms are directly connected to the part of the brain that is affected by the vascular problems... so each will be a little different. Declines tend to be connected to vascular difficulties rather than a pattern like Alzheimer's.
So try to get that chest x-ray and get the therapist report and see what they have to say before you guess at the cause. It could be something as simple as spring allergy drainage if she has allergies.
Question... is she losing weight?
I didn't give many answers but hope something here helped.