Can confusion caused by a UTI be permanent in an elderly dementia patient?

I would suggest the confusion to which you refer is in fact delirium. Sorry to say it can last for days, weeks, even months. My mother has had a series of UTIs both before and after going into a memory care unit. Each attack is quickly knocked over with antibiotics, but the delirium is taking longer and longer to move on each time.
The problem with dementia patients is that it is difficult to know what is ''normal'' dementia confusion and what is ''normal'' delirium. If medical people find it difficult to work out the difference, no wonder we carers have difficulty understanding it.
About the only thing I can suggest is in future to closely monitor the patient, if there is a sudden downward trend in confusion then check for a UTI. On this forum you will have noticed a lot of posters' first suggestion is a UTI in any change of behaviour. While the causes for changed behaviour can be endless, it is a very good starting place for investigation. Likewise for constipation.

It can take a person with Dementia much longer to return to "normal" or what was "baseline" And they may never get back to that point but there should be some improvement.
Hydration is key also to help prevent the UTI from returning but to help keep all organs with the fluid they need.
Weakness can be helped with just trying to increase daily activity. A little bit each day, or several times a day getting up and moving about. Just like PT would do. This is not just walking but even playing catch, tossing a beanbag into a bucket, putting clothes pins or clips onto a curtain and taking them off.
But all of the declines are "expected" can not be prevented so we must be prepared for them. You learn to work with a New "normal".

Then have the UTI test run again. Sometimes you will need another type of antibiotic

I have found that a daily capsule of cranberry concentrate (4600 mg equivalent) has helped prevent more uti for my dad. He had three bad ones in the year before(hospitalization required) and his sudden delusions and fever were the symptoms. Yes it took longer to return to “normal” each time.

When my mother was in the nursing home, she had a UTI. I was following up with them. They are suppose to put the patient on an antibiotic and wait for the 3-day culture to see if the patient is on the right antibiotic for that specific UTI. However, my mother wasn't getting better but she just happened to fall out of her wheelchair and hit her head and made them call EMS & take her to the Emergency Room at the hospital. They said she still had a UTI and the nursing facility had put her on the wrong antibiotic and did not follow up after the 3-day culture!!! So beware and always ask about the "cultured test". My poor mother suffered with that for 3 whole months because I believed they had treated her properly and they had not.

If her infection has cleared - get the results from a culture to make sure - she may have some slight kidney damage. Her injured kidneys don't function as well as they usually do to clear her blood of waste products. This could make her weak and a little confused. Usually, confusion clears when UTIs are treated correctly.

Does anyone else have good results with cranberry juice to prevent or help UTI's? Back in my days of no insurance and no medical help, "Drink cranberry juice" was the "go to" routine. I don't know if that works as effectively in older adults as it did for hippies with no medical insurance, but it might help some.

Yes, confusion and extreme irritability can accompany UTIs in the elderly. UTIs can also result in high fever, and sepsis. It is an emergency. It can be fatal.

Yes it happened to my Mother, everyone said she would get back to normal but she never did! She woke up one day 3 years ago living in the 1930’s. I became her sister and it hasn’t changed. She calls me by my right name but I am her sister not daughter. That was only the beginning!

My stepmom developed a UTI which caused delirium. She thought my dad was trying to kill her and refused to stay in the apartment in assisted living with him which in turn made my dad extremely upset to the point he was in tears (they both suffer from Alzheimer's). It took two different antibiotics to get rid of the UTI but she also developed a yeast infection from the antibiotics. Called her doctor and got her medication for that but it took a couple more weeks before she was completely out of her delirium.