The nurse said it's impossible to get a cleans sample with an indwelling catheter. Is that true?

Hi, my mom has dementia. because of a stroke a year ago she has a catheter. she has had numerous infections over the year which has decreased her cognitive ability. I am concerned she might have e-coli or another type of infection tht the antibiotic is not effective in treating. (the way we found and treated the e-coli last time was through an er visit and a return to the hospital for IV antibiotics.). The nurse at the urologist says its impossible to get a clear sample because she has the catheter. Is this true? her behavior has gotten so much more violent recently. the dr has ordered a medication change to introduce depakote which combined with the seraquel makes her sleep constantly and she is still aggressive, Please help.