Took in Extremely unhealthy boa, need some advice

[Akuryai]

Hey guys, havent been on in awhile. Anywhoo, I was told from a friend that a guy had rescued a Red tail boa, and was giving it away free to good home. And yes, I knew beforehand the snake was unhealthy, but my god, some people shouldnt own snakes. Whoever he rescued it from, must have had a mental illness. This snake is 5 years old, and she is only 4.5feet long, has a scar on her head from a rat bite, and her ribs are showing. Im surprised at how tame she is, considering her abusive past. Im just curious, is there anything I can do to allow her to atleast get some meat back on her bones? Besides a higher rate of food. Maybe some kind of medicine? I plan on nursing this snake back to full health, making her a great member of my family.