UTI's and D-Mannose

Callie, maybe?  DD's older Basset has chronic UTI problems and is now at the Vet's with fluid on the lungs, bad UTI,  and was recently diagnosed with a heart murmer.  I suggested she ask her Vet about giving her D-Mannose, but know nothing about dosing it or how to use it.  I'm hoping her Vet is familiar with it, or at least willing to look into it.  I know mine wasn't with Winnie.  So I'm looking for further information to give her.  Thanks!