Thanks for posting on EmpowHER's community!
It does sound like your sister has a lot on her plate! Despite all her responsibilities as a caregiver, it's important that she does get rest to stay well. Especially during her cold, I hope she is getting enough sleep. That's good she is taking medication for treatment which will hopefully get her better soon!
To clarify, are you asking if a urinary tract and kidney infection can cause death?
When a urinary tract infection is not taken care of properly, it is possible for the infection to spread to the kidney, causing kidney infection or possibly even sepsis which can be deadly. A kidney infection can be much more painful and cause more sickness than a UTI.
Sepsis is sometimes called blood poisoning and is essentially the body's response to a serious infection or illness. Typically, people do not die from a UTI as they are very common. But if not treated correctly, it can spread and lead to septic shock.
Did your sister treat her UTI? There are some very inexpensive over-the-counter treatment options for UTIs which are effective.
I hope your sister gets well soon!