What Causes Recurrent UTI In An Elderly Woman?

my 86 year old mother (dementia and stroke 4 yrs ago) has recurrent uti s. what line of therapy is recommended. we have had her on various antibiotics and she still gets uti s. I give probiotics, d-mannose,cranberry. she started Flomax two months ago, they said for urine retention ( only 117 cc post void on scan.) I think too little to say retaining, they wanted catheter in her. she gets toileted and is inc and cont at times, more so inc now that she takes Flomax and started Lasix for new dx mild CHF. I am torn, np s who come to house , are not following what they recommended in past for nps change. they were to put on low dose abt. so my mother suffers thru uti until she gets treated short term and strted w another uti.