Suggest Treatment For UTI

Hi, My mum aged 85 has just been discharged from hospital, went in with very swollen left leg, red, blotchy, itchy skin,venous dermatitis diagnosed-scan for dvt negative. She has a urinary tract infection-which is not being treated as allergy to most antibiotics and even more tricky as on warfarin. With bed rest the swelling reduced but this cycle has been reoccurring for 3 years now. Right leg subject to venous unlcers, often healed for a short time and then another breaks out. Mum excercises and is active despite this. She wears compression stockings when she can get them on. Takes blood pressure medication and Lasix when required. The swelling and aggrivation from itch/burn worry mum mostly-cold compress and aqueos cream are all she is using now. Any suggestions or help would be appreciated. Jasberry