Good morning Beth,
Does your aunt take any medications at all?
Does she seem to be uncomfortable when she goes to urinate? Any fever or chills?
How was her pulse on the monitor?
Ok, thanks for the additional info.
It is really hard to tell with elderly people if they have UTI, especially since your aunt doesn't even complain about anything. Often, with UTI, older people will not have a fever but they will go more frequently and have less volume every time they go. Also, it is usually uncomfortable to pee because of the burning so if your aunt is not making uncomfortable faces or moaning while she pees, I don't think she has UTI.
It just sounds that she has less urine because she hasn't been drinking as much as usual. I don't think you should be concerned about that. If you notice that she is uncomfortable while peeing or if she pees much more frequently with lesser amount (I am not sure how you can measure it if she uses depends), then I would be concerned for UTI.
Her blood pressure is definitely very low but it sounds that it is your monitor. Usually when someone has such low blood pressure, their pulse will go up to compensate for such low numbers but since your aunt's pulse is normal (70 is normal), I think its your machine. I would ask the nurse to come and double check on her blood pressure though. Try to have her drink more fluids today to see if she pees more and if her blood pressure goes up. If she doesn't want water, maybe you can give her a lemonade or sweetened ice tea.