You may want to make an appointment with her doctor to discuss this. A medical diagnosis is the key to understanding these changes. Many older adults are taking drugs or need new medications during their hospitalization. She could be having a reaction to one of these.
Delirium is a common problem in older adults with hip fracture. It's different from Alzheimer's. Delirium is the sudden onset of confusion. There may be a loss of consciousness and attention. The patient may ramble or say things that don't seem to make any sense at all. It usually doesn't last but can have long-term effects.
Dementia is a decline in memory and thinking abilities. Alzheimer's is just one form of dementia. It's unclear what brings dementia on. Infection, dehydration, or drugs can cause delirium. These are treatable problems.
There may be some things you can do to help your aunt. Talk to her slowly but clearly in adult terms. Tell her what time and day it is. Remind her who you are and why she's in the hospital. Make sure she can see and hear if she uses eyeglasses or hearing aids. Put a large clock where she can see it. Besides talking with the doctor, ask the nursing staff what you can do to help. With a team effort, you may see your aunt restored to her old self.