I suggest she get to an emergency room. Alzheimer's patients die from falls and hip fractures and also from pneumonia due to immobility. Anytime she has a major incident like a fall it is best she be checked out by a physician to be sure nothing damaging has happened to her. Waiting a long time before having a problem looked at could spell trouble, because a small issue can grow into something much worse if left unattended. It may be nothing, but you will sleep better knowing you did the right thing by having her checked out properly. Best of health to her!

Hi Sue,
Alzheimer disease makes a patient more vulnerable to falls, these patients must be monitored to prevent falls. The disease progresses at slow pace, if you find a sudden deterioration there might be some additional problem like brain stroke, infections like, pneumonia, urinary tract infection, sepsis etc to cause this type of sudden change.
Your mother needs an urgent medical attention for the paining bruise and for the HIGH POSSIBLITY OF FRACTURE AT HIP/SPINE. Fractures are very common in elderly.
Please don't make her bear body weight till fracture gets rule out because it may dislocate the fracture.
I hope that answers your query.