I had felt one coming on myself two weeks ago and i was able to stop it in its tracks with homeopathy. My yorkie had similar symptoms months ago and i was able to heal her with homeopathy. Im not sure if you have utilized it however here are some remedies of course the symptoms are based on a humans but you can look at her and kinda tell how she may be feeling.
Apis mellifica -- for stinging or burning pains that tend to worsen at night and from warmth. People for whom this remedy is appropriate feel an intense urge to urinate, yet can only do so in drops
Aconitum -- for early symptoms of UTI, particularly with extremely painful urination that is often described as a hot sensation
Berberis -- for UTIs with burning or shooting pain during urination that may radiate to the pelvis or back. When not urinating, an aching sensation is present in the bladder that worsens with movement. Pains may also extend to legs and abdomen
Cantharis -- this is the most common and considered the most effective homeopathic remedy for UTI. This remedy is most appropriate for people who are restless, experience a burning sensation and decreased urine flow (despite a strong desire to urinate), and have increased sexual desire despite symptoms
Mercurius -- for burning urination and a strong urge to urinate. Symptoms worsen at night and tend to be accompanied by chills and sweating. Urine is dark and only small amounts pass. Burning sensation is often worse when the individual is not urinating
Nux vomica -- for people who have a constant urge to urinate. Pain is described as needle-like. The urge to have a bowel movement may accompany urinary urgency. Mild, temporary relief may be experienced from urination and warm baths. Symptoms may begin following ingestion of alcohol, coffee, drugs or overeating
Pulsatilla -- for bladder inflammation that begins after an individual develops a sudden chill in hot weather. This remedy is most appropriate for people with an urgent desire to urinate who may be emotional, crave attention, and dribble urine after laughing, coughing, sneezing, or being surprised
Sarsaparilla -- for women who experience severe pain at the end of urination and who, occasionally, may feel compelled to stand to urinate
Staphysagria -- for UTIs usually associated with sexual intercourse or following extreme embarrassment or humiliation, particularly from sexual abuse. This remedy is most appropriate for those who have an urgent desire to urinate and have the sensation that a single drop of urine is still present even following urination
If you do end up puttiner her on antibiotics make sure to up her probiotics LOTS as the antibiotics will not only kill "bad" bacteria but the good as well then causing future candida issues etc. probiotics will also help to boost her immune system
You can also add foods that are rich in phosphates and magnesium.
Hope this helps.