Pregnancy chance and related health question

My and my Girlfriend had sex yesterday, and her period would typically begin within a few days from now (right around the 24th) knowing this and the fact that i did not have a condom we elected for just anal penetration.

No vaginal penetration occurred whatsoever, and there was no ejaculation on my part, only precum was present. I hadnt ejaculate that day at all, no masturbation or anything that day, and i showered that morning. I dont recall but i may have masturbated the night before. Is it possible that semen could have been present in precum that long and post shower?

Also, this morning she told me that she is experiencing some light pink discharge, and a burning sensation in her vagina, I believe implantation bleeding shouldnt occur till roughly 6 days after becoming pregnant, so it sounds to me like it may be a UTI? i know this is a risk with anal sex without a condom, but as i said no vaginal penetration occured which is usually the cause of a UTI after anal sex (double dipping so to speak).

I told her to keep an eye on her temp and if she develops a fever to go to the doctor
Also note that a pregnancy right now would be a pretty terrible thing, and she would feel better if she took a morning after pill but wouldnt be able to do so till roughly 48 hours after.

Is the morning after necessary or given the circumstances is there basically no risk involved at all? prompt response will be very much appreciated