Of course the obvious would be something like Desitin or other diaper rash cream. Put some baking soda in her bath water. It helps neutralize acids & soothes the butt. Is she on an antibiotic by chance? Could be a candida rash instead of a typical diaper rash. That would be helped by an antifungal on the butt & yogurt to eat.

ETA: the candida rash is the yeast rash @lifeisgood is talking about. Posting at the same time!

A pediatric nurse told me to use desitin maximum strengh w/aquafor over it to seal it on and keep diarrhea from sticking. It worked for us. hope it gets better soon.

If it is yeast related Canesten cream is safe to use in babies.  My DD had a severe rash that looked like little pimples all over her hooter and bum, and the doc told me to put Canesten on it.  It cleared it up within the day.  If nothing else, I don't think it would make it worse to try it out.

Oatmeal baths helped my youngest.  He would get horrible diaper rashes only when he was teething along with the runs.  I also used Desitin.  Not the Maximum strength cause that seemed to make it worse.  The regular strength.  I would also caked it on and of course changed his diaper frequently.  

OxiMOM said:

I have a friend who's son had a rash that would not clear up no matter what. She eventually switched to cloth diapers and it cleared up.

Yeah my firstborn was like that.  couldn't handle disposable so I only used them when I HAD to.

Put slightly moistened tea bags (any kind will do) in your wee ones diaper. It not only helps heal the rash, but helps soothe it, too. Pull the strings off, though. I usually put two or three in there.

I too would not wipe if they had the runs, just pop them in the tub and rinse with warm water.  Then let them air dry for a while for sure.  Definitely need the barrier cream before putting the diaper back on, I used Zincofax or Butte Paste.  My daughter used to get bad rashes from diarrhea too, hope it clears up for you soon! 

DS had a terrible peeling, weeping rash at one point. We were instructed to use a combination of prescription antibiotic cream and lotrimin athlete's foot cream (NOT the spray, ouch!) at each diaper change. I also used my perineal irrigator bottle that I got in the hospital to hose him off after poops so I didn't have to wipe him and aggravate it. I just patted him dry and slathered on the goo.

if its bc of diahhreah as it sounds, I would suggest an oatmeal bath, a&d ointment coupled with extreme amounts of baby powder or corn starch. Always worjked wonders in exploding ass cases

Anti monkey butt is great but u can put plain yogurt on booty if yeast is suspected to be the culprit. Its a natural way to go. Also air will help so much. Lay out some old blankets and let her on them. I know the squirts make it hard. Maybe let her on an easy to clean tile floor...

I can not express this enough with rashes... CHAMOMILE TEA BATHS!  

Get a big pot, fill it and bring to a boil.  Tie about 10 tea bags together and toss them in!  turn heat off and let sit until cool enough to carry to tub without spilling and causing major burn injuries. GOD forbid. Add tea to bath water and let your baby soak!  Repeat the next day or multiple times a day if needed.  It sooths and heals my son's eczema, sun burns, rash of any sort and makes the baby's skin and hair so so soft and is chemicle free!  It also soothes upset tummies when sipped on.  You can even keep some on hand and wipe baby's bottom after every changing.  I swear by this!  I hope it helps!

When my son was potty training he got a wicked pimpley rash on his bottum and privates. It would not clear up. Took him to dr. And was told he had a staph infection on his skin. Apparently its common in pooty training toddlers. Antibiotics helped. But my dr. Told me to go to the drug store and buy dom boro powder mix. U mix it with warm water, soak a rag in it and apply compresses to the bottom. Worked great. My son has severe food allergies that affect his skin so we have had to deal with all kinds of rashes

In the hospital NICU we used Mylanta or Maalox antacid mixed with a really thick rash cream like overnight Desiten. It really dries up the rash quickly, I've also mixed it with cornstarch and had good results. It will be hard to heal until the diarrhea is gone. Remember the BRATTY diet. Bananas, rice, apples, tea, toast and yogurt. 

The worst rash I saw was on a kid at the daycare I worked at. She came to us with it. Poor little girl. She was 8 months old and had a rash that had open bleeding sores on it. She came with a prescription tube of something , I wish I could remember the name though. We used that and vasaline every change and only clear water on a washcloth. We tried to be a gentle as we could, she was already in a full body cast. It was for a broken leg. The cast started under her armpits and went down to the middle of her calfs. There was a small opening so she could use the restroom. Changing her diaper was a two person job. Trying to keep the cast clean and dry was hard. Trying to keep her entertained and happy was hard too. Her femur was the bone that had broken, her dad claims it just snapped when he was changing her diaper. Yea like we believe that. Last I heard they lost all parental rights to her her older sister and brother. They brother an sister went to two diffrent aunts. She was staying with an aunt but as soon as they decided not to give them back to the parents that aunt dropped her into the system. I saw her and her brother and sister for a second ( long enough to say hi and how are you) about a year ago. They see each other at school and after care. The baby was in kidnegarden and such a happy little girl.

Borofax really does work really good and if you can get a hold of it get it! A lady gave it to me for my ds and i never could find it to buy myself! It really is the best! Also there is this oatmeal bath powder you can buy and it also works great!