So sorry to hear about your family's loss. in my support group, we often hear from caregivers who say that the spouse left alone by the death of their partner soon exhibits deeper signs of dementia.
Often, I suspect, that is because their partner has shielded them from others knowing the real extent of their condition. It becomes apparent when family members are much more in their company. But i'm sure too that the emotional loss and the life changes are a a huge blow. dementia always gets worse when other factors occur -- losses, other negative events, maybe health issues such as minor strokes.
i'd certainly recommend you have her doctor check her out -- things like small strokes, urinary tract infections, undiagnosed pains they can't communicate -- these all cause a downturn in dementia conditions. so it's worth the doctor time to make sure. if it's only meotional shock, she may gradually improve a little, though probably not fully. you know, short-term memory loss is due to dementia so she isn't forgetting you for any other reason. and you haven't forgotten her and that she needs your love -- so, there's that. to know more about dementia, take a look at my newest book, "Speaking Dementia" by Frena Gray-Davidson , available on amazon.com. you can also read inside it for free and i deal with many of these kinds of questions in a cheerful practical way that is not depressing, though i say it myself!