Have you tried cutting out all citric acid? My daughter would get blisters and always had lose stools...still does really but she's not in diapers anymore so no blisters.
I could not give her any juice or anything with high acidity. Very little sauce on pasta. So forth. I also had to put baby powder (making sure not to get dust floating around for her to breath) in her diaper every change.
She never got blisters that big, but she did get them about the size of the end of my pinkie finger and they bled. I also sat her in bath water with baking soda to soothe her poor sore bottom if she did have a bout of the "hershey skirts" as my baby brother calls them.
My daugher is very sensitive in many ways. I think she just produces too much acid and when I add more to her diet it is too much for a diaper bottom. She gets sores in her mouth from time to time when she frets about something. She's a worrier like mommy.
I would start to potty train her for one so that she doesn't have to wear diapers anymore. Start with a day in the bathroom nakes so she can figure out what you mean when you say pee pee or poopies. Maybe do two if you think she hasn't gotten it yet.
Then buy cloth panties...let her pick some out. Buy lots of carpet cleaner. Carry the potty chair around with you every where. Remind her constantly to tell you if she needs to go potty. Give her a little chocolate chip if she makes it.
Should take a few days and then you won't have that issue anymore. Also explain if she poopies in the potty it won't burn her little bottom and it won't hurt anymore. That might be good motivation.