How can my mum (92) overcome UTI when errant primary doctor's Sulfamethox script made it worse?

Her reaction mimics stroke, Asthma. Two Hospital visits in May: first for dehydration and lethargy. Several days then released. Her primary talks to me long-distance (I just returned from six days in the house I was raised in with mum and her full-time live-in Home Attendant) and asks if Mum is allergic to sulphur? Not that I know of, but isn't that POISONOUS? He prescribes sulfamethox, to which Mum has allergic reaction which mimics Asthma and a stroke (which was not diagnosed in hospital). Back to Long Island Jewish Hospital AGAIN! The question are: do I have a lawsuit? Isn't there a better antibiotic than the sulfa stuff? Is this common (as many friends of my age who have experienced this similarly) indeed with a 92 y.o woman and can Mum rebound - and what med really NEEDS to be prescribed. Honestly, I feel like the doctor and the hospital experimented on my Mum and made her worse! I need some answers and maybe a lawyer? What does the community think, because I talk to people, from the cashier at the supermarket to friends at the Pub who say they had similar experiences and it is the UTI which is making Mum act weird now. Mum has lost the use of her legs in the past three weeks! Cannot sign her name; cannot hold the phone and speech is intermittent. I will love you and appreciate any advice or similar experiences you can share to enlighten us and possibly same my Mum, the former school teacher for fifty years...Yes, she had dementia, and HBP by the way.