Janine, I'm so sorry to hear about the situation with your mother.
Regarding your mother's discharge: if you feel you cannot provide the care she needs, for whatever reason or reasons (and I'm not judging you, no matter what your answer), then be clear that you will not permit her to be discharged home to your care. I think the correct phrases are "vulnerable adult" and "duty of care" and please remember you are not obligated to provide care. Stay firm about what you can and cannot do. For better or worse, perhaps her medical condition will prompt her needing rehab or medical care or OT modifications at home. I agree steps are a concern, as is safety in general. I hope you can feel sure she will get the care she needs
Regarding the difficult day you had: I experienced something similar while my mother was in hospital (for about 12 days, sectioned following being found wandering, injured, hallucinating, and confused). There was one day where she was incredibly, horribly nasty to me, just dripping poison. On other days she was confused but pleasant. With the staff's encouragement, I was able to reduce my visiting time from all day, every day, to shorter times, and eventually, not every day. However, I had no concerns about the care my mother was receiving, which I know is not the case for you.
So what I'm trying to say is that yes, it's likely the dementia, coupled with the damage from the strokes, and made worse by being in hospital. People with dementia notoriously don't do well in hospital: too many people coming and going, intrusive procedures, staff changes, medication changes, nothing is familiar and it's often just not a good place for them to be, but of course the situation demands in. Often they are just anxious, upset, or plain old scared. I'm sorry.
I do NOT think this change in her behaviour is your fault or anything you have or haven't done.
My only other thought is if your mother could be in pain or physical discomfort of any sort. I know it's tricky with a dementia patient but there are pain assessment scales that can be used even if a person is nonverbal, so you could ask the nursing staff to check this out on a regular basis.
Will be thinking of you and hoping for the best.