Hi N.,
I swear by cranberry juice...it is awesome and has always done the trick for me.
Of course, I don't know how long your mother has already let it progress. Ever since I've discovered the cranberry juice thing, I've been able to stop mine fairly early on.
Also, I'm not a doctor. But...I'm not so sure that your mother taking something to keep her from going is going to help with the infection. It may even make it worse, or perhaps combat the cranberry juice effect if the importance is to let the juice run all the way through the system multiple times.
Plus, our bodies tend to do the things they find necessary to combat whatever is troubling them. So, going more often may be one of those. Yes, she may find it uncomfortable to go a greater number of times, but it's better than allowing this infection to progress to kidney issues. Unfortunately the old adage is probably true here: no pain, no gain.
And, if this natural method doesn't work for your mother, I agree with another poster who said to take her to a clinic. Bladder infections are quick and easy to diagnose and a prescription can be given...not your most expensive clinic visit, for sure (not compared to what it could turn into before October!)
I hope this helps!!