On one hand, herpes symptoms can be highly variable. So the literal answer to the question, as posed in the title of your thread, is yes, I suppose it could be herpes. But it really doesn't sound like it. I can't comment on the "small rash" in her genital area - but if it looks to you like ingrown hairs or pimples, I suppose that's what it probably is.
But most important, if your partner has symptoms of a UTI, that sounds like a good bet. The symptoms you describe for that sound compatible, but not quite typical; but if she has had UTIs before and has the same symptoms now, that's probably what it is. UTIs often are triggered by sex--not an STD, but because sex massages genital area bacteria into the urethra. The historic term "honeymoon cystitis", not used much any more, tells it all: UTI associated with increased sexual frequency.
Bacteria that are normal resident in the rectum (like E. coli) often colonize the vaginal area and then cause UTI. To my knowledge, research has not associated UTI with anal sex (which is what I assume you mean by bacteria "from back to front"), but that may be just because researchers haven't asked the question, and I am certain it contributes to movement of rectal bacteria to the vaginal area and increases the risk of UTI. Heterosexual couples who practice anal sex should wash with soap and water before moving from anal to vaginal sex; or perhaps use a condom for anal sex, then remove the condom before vaginal.
The standard, bottom line advice applies: Your partners needs to see a health care provider for diagnosis and probably treatment. If that provider thinks herpes is possible, then perhaps diagnostic tests should be done in you and your partner. But I doubt that's the problem.
Good luck-- HHH, MD