Has she been to the doctor for this? Perhaps it's a strong allergic reaction to the acidity in tomato products that has just been inherited. They do have topical Benadryl, which may help. Does she take bubble baths or shower? I would think taking baths may irritate the condition more, or at least use a mild soap and this might give her some time to get over it.

Hope she feels better soon!

What goes in, must come out and usually it's not a problem. Sometimes it may be. It's probably, technically an 'irritation' or contact dermatitis rather than an 'allergy.'

Painful red rashes anywhere produce even more sensitive skin. Pain relievers in general can help (tylenol, ibuprofen) some. Drinking lots of fluids might help dilute at least certain excretions which may help a bit. Air drying, as little touching as possile except to rinse and maintain hygeine, and possibly something like lanacaine (look in the pharmacy section for products designed for that part of the body, and which are designed to be soothing and pain relieving). When in doubt though, as little touching as possible is likely best.

Drinking lots of fluids is going to be a hard sell usually in situations where urination hurts a lot. There are different ways to explain how this works. One visual would be to add food colouring to water, and imagine that colour is what causes the hurt. Double or triple the amount of water and it's easy to see how much less colour there is. Dilution as a concept can work too, if she understands that. Just be very supportive because that first time she might try this, it will require a little leap of faith and trust on her part (and it will probably help and it won't hurt; but it probably will still be painful for her compared to 'normal').

do consider a consultation with the doctor though because sometimes antibiotics are not effective against certain infections and it's hard to know sometimes if that's the case; or if maybe more were required or something

I learned the hard way about tomatoes when I was nursing my first born. Almost all of her diaper area turned bright red as if she had been burned--it was hot to the touch and hurt badly. Happened so quickly, and the area was solid red, no area was spared. Then I read that tomatoes and chololate inn the mother's diet can cause terrible diaper rashes. It took a few days to heal, even when I skipped using a diaper and exposed her bottom to the air all day. I would try the benedryl and maybe some over the counter cortisone cream.

Try some Desitin or A&D ointment. It will protect the skin from the urine and give it a chance to heal. Think of it as diaper rash! Powder it to keep it from smearing all over her underpants. Should feel pretty soothing, too. My dd has numerous food allergies and they affect her bottom this way, too.

DD has dye allergies. The rash on the bottom was worse when she was in diapers and the poop (or pee if she drank liquid containing dye) would practically burn her little bottom. She was 2 before we figured out that it was dyes she was allergic to.

Now that she's potty-trained, it still makes her red, if she eats some food with the dye, when the food comes out the other end, but at least it is not as bad, since she doesn't sit in it anymore. Plus - we know what foods to avoid (although it's hard to police her everywhere).

Benadryl will help if it is an allergic reaction but not sure it will help if it is sensitivity to the acidic food. I would call the nurse at the doc's office if the Benadryl doesn't work, and ask what they might recommend.

Also - you may already be aware, but you should avoid bubble bath products. And should also do the shampoo part of the bath at the end, to minimize the length of time she sits in bath water with shampoo in it.

My daughter had a similar problem when she was little. The doctor had us use cortisone when it was really bad. The rest of the time we used A&D. Her reaction was caused by "fake" cheese, like cheezits, goldfish, etc - of course they were her favorite snacks!

My two DD's used to get a diaper rash from carrots- I could always count on a sore bottom after they had them. Not too bad or anything, just a little red. But DS never had a problem.