I've read both of your questions.
I'm really astounded that you have dealt with this issue and the wiping issue for 4 years and you have just given in to her tantrums on all of them. You have to ignore tantrums. All kids do them over something - but they get over them because parents ignore or send them to time out or whatever. They don't keep caving in. The tantrums are working, and apparently (per your other question) to the point that your almost-8-year-old is wetting herself rather than pee and wipe.
So this is an entirely unhealthy situation for everyone involved. This child is running the household, and your younger one is seeing it.
This should have been discussed ages ago with a pediatrician. It may be due to some compulsion, and if not, it may have escalated into an unbreakable habit or even a psychological disorder after years and years of your child getting a pay-off for this behavior. So ask the pediatrician for a referral to a child psychologist who can figure out the underlying reasons, and work with you on more effective parenting techniques that will be consistent.
So, no, you should not be kissing a 7 year old's "boo-boos". You're not helping her at all. She has got to learn to function in the world without having a tantrum, and you seem helpless to stand up to her. This is going to affect her in school, in life, in the family, and in her psyche if you don't address it. Surely someone has suggested this to you in the past 4 years, right? Why have you not listened?