Ah ok. You can lead a horse to water but can't make it drink.
At least you're understanding the difference between thriving and surviving. Under proper conditions that snake could have lived 25+ years.
My best advice, get your snake away from hers asap, quarantine yours and let her take care of hers.
When she sees how well yours is doing maybe shell open her eyes. But who knows? Ignorance us bliss, or so they say.