They would be able to detect it. They'd ask you beforehand if it's possible you are pregnant and I think if you say no they won't test for pregnancy, but if you do happen to be pregnant and also have a UTI you'd only be able to take certain medications for the UTI. So overall you probably would want them to test and make sure so if you are pregnant you don't hurt the baby

You could be putting your unborn baby at risk by not finding out as not all medication is safe to take. Can't you go into the doctor on your own? ask your mum to wait in the waiting area

when they test for a uti it doesn't detect pregnancy. they would need to do a pregnancy test. they'll ask if there is a chance you're pregnant. if your mom knows you have sex just say "well I have sex." the nurse will most likely test.