This snake needs a vet. Most vets are understanding that I've dealt with and have known- the injections she needs to stop the infection in its place then push that infection out isn't a lot of money. $12 a shot and it's worth it. $120 to save your snakes life. I understand some people can't afford this, but in my humble opinion if you can't care for any animal when it's I'll ( especially due to neglect) you shouldn't own an animal. I know it's not yours and praise you for trying- any animal in your dads care should be removed immediately and put into some rescue where the snakes can get proper care.
I hope you have quarantined this girl from your other snakes. It's highly contagious as others have already mention.
It looks as if her eyes are infected, meaning the infections spreading - pretty quick if this wasn't this way a couple weeks ago. The rate of the progression and the gunk that built up is crazy. Poor girl.
Sorry for being so harsh, but this is the worst case I've seen of mouth rot. I pray she makes it without the required IM (intramuscular) antibiotics she needs to fight the infection.
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