Apple just finished 5 day course Nitrofurantonin on Tuesday, seemed to do the trick - however I took the added precaution of using Waterfall D manose powder morning and night after and today am dropping once to take nightly for few days. It is my second UTI since June.
While I don't use your HRT, I inceased my Vagifem every 2 days and instead twice weekly am keeping that up next week I think..
I am 7 years older but wonder if maybe a more localised pessary might help (like Jules suggests also).
As for the UTI, I always kick myself because for me I feel it is a lack drinking water and when travelling not stopping enough times for comfort breaks. Lastly buy some bio yoghurt like plain Yeo Yalley as help keep good bacteria in gut which AB's can strip away and thrush can come along.