Sorry to be blunt but rescuing and rehabbing any creature let alone one considered an exotic is tough and can be a "tragedy in the making" if you aren't fully prepared to deal with any eventuality. That might be sky high vet bills, making the tough decision to euthanize if all else fails, extremely strict quarantine measures, weeks or months of working slowly with this snake to get it back to full health. It can also be a walk in the park and everything can go beautifully but the fact is you cannot know which path you'll walk with any living creature, let alone one that's been poorly cared for.

If you aren't ready to commit fully to whatever the situation throws at you then perhaps you may want to recommend this owner place the snake elsewhere or help them locate a herp rescue in your area.