Any ideas on how to keep a bedridden patient from having bowel movement enter her causing a UTI?

I’ve been doing this for my mom for about 3 1/2 years. I learned how to anticipate bowel movements and have her turn over stomach down on a clean chux. Then I coach her to push into a clean wipe and I catch it before it travels down to her vagina. After I clean her bottom and she’s done, I apply barrier cream the opened diaper and I move back to the other side of the bed and I have her turn back over onto her back and the clean diaper. Hope this helps!

If she is on somewhat of a "schedule" if you can get her onto a commode or into the bathroom to use the toilet it would make it easier to clean her.
Using a Hoyer Lift makes it easy to get her onto a commode or into the bathroom. The slings with the "commode hole" make it easier to clean someone after toileting. It can also be used while in the shower. (the mesh sling is easy to wash and dries quickly)
Actually not to give an anatomy lesson here it is the urethra that you want to protect from fecal matter. You can provide some protection by using a barrier cream, just a very light bit, patted on not rubbed in. And obviously when you are cleaning wiping from front to back is important. And using PLENTY of wipes. I used to use a LOT of wash cloths to clean my Husband before I would start using wipes. I could get more removed with a thicker wet cloth than the thinner wipes.

Your wife needs professional nursing care. Too many UTI's can cause serious complications. Some could kill her, like a blood infection or a kidney infection.

I had to hire an aide to come put my completely bedridden husband on the bedside commode every morning so he could poop. It worked out really well as she would hold him up when he was done and I would wipe him and clean him up. It made my life so much easier than trying to clean up poop while he was lying in the hospital bed.
So if your wife is on any sort of pooping schedule, you may want to hire an aide to come at that time to put her on a bedside commode.
I wish you the very best, as I know this is not only hard on you, but her as well.

UTIs are extremely common in elderly women and are not always caused by hygiene problems, but by age-related physiological changes that prevent the bladder from fully emptying. I have had good success cutting down the number of UTIs my MIL gets in LTC by having the staff give her maintenance D-Mannose, a supplement that is a simple sugar and not known to interact with any medication, nor can one be "over medicated" on it. Once your wife is clear of her infection you can start giving it to her every day. It won't prevent UTIs 100% but should help quite a bit. FYI I'm not a proponent of supplements but we were desperate to get her some relief. This supplement was recommended on this forum and I credit it with giving my MIL relief. I order it on amazon.com.