9 year old undersized Ball Python rescued - now what?

Hello, all, this is my first time on this forum and I come bearing questions... here is my situation:
I found a ball python on kijiji that needed re-homing due to owner's disinterest, basically, and when the lady described it to me I was beginning to suspect some neglect, because she said they got it for her daughter about ten years ago, but that it is only three inches wide in the middle, they have never weighed or measured her, and fed her only one mouse per week.
When I saw her, though I was in the market for a fully grown female I had to take this baby, because she is so severely undersized for her age - I consider this a rescue as they had NO under-tank heating (a five inch heating rock at one end on the two-foot aquarium was the only heat they had given her,) NO humidity added at all, and a tiny tiny bowl with a hole cut in it as a hide, bone dry wood chips that used to be forest bark but smelled like urine and cigarettes - owners were smokers. I could go on all day with how mad this makes me.
She is the width of an empty paper towel roll at her widest points, and is only about a foot and a half long. I didn't know a snake could be stunted so drastically in it's growth but I intend to fix this and spoil her rotten for the rest of her days.
QUESTIONS:
1) I am going to feed her today, was hoping to give her two adult mice if she will take them, and three a week from today, frozen/thawed and warmed... Does this sound like the right amount? I wasn't sure about feeding her 3 right away / if it would be too hard on her digestion? She has never had more than one mouse at a time before. Any advice for feeding her long-term, if my aim is to encourage healthy growth?
2) She has been getting used to her new home for several days, it is a glass tank about 3 1/2 feet long, with humidity and temps perfect, multiple hides etc. (she loves her first warm hide EVER! ;)).. I have never had a ball python before though, (just corns and garters,) and despite my reading extensively about them, I am nervous that something will be not-perfect about her environment/care, given her unfortunate past... any specialized advice in this regard would be very much appreciated.
And of course if anyone has any other thoughts about her past or future, advice, etc. please share it, I am open to constructive criticism and whatnot, as it will benefit my baby, who I have named Odette. Thanks very much! :)

Certainly a mouse a week is not sufficient. Based on the girth you described, she should be eating large weaned rats or small rats. Do you know if the mice she was eating were live or frozen/thawed? You'll want to start off feeding her the same thing. I'd give her a week to adjust to the enclosure - no handling, no feeding. I think giving 2 mice is fine. Let her finish the first one and try for a second one. Eventually she will need more than 2 mice, so you'll want to try and convert her to rats at some point. Leave her in the tank when you feed her, but never leave her unattended with a live mouse or rat.

As for your setup, you didn't provide any details. I'm assuming you're using an under tank heater. This should be regulated with a thermostat - thermostat probe should be directly attached to the heat mat. You'll set it so the glass on the inside of the tank (hottest part she can touch) does not exceed 90-92°F. You should have hides on both the cool and warm side of the tank. Humidity 50-60% is proper. What substrate are you using? Don't use a heat rock - since she did have one in her other tank, you should inspect her for any burns that may require treatment.

And welcome to the forum and congrats on your new snake :)

The heat rock is bad but UTH is not required.
I see no problem with a mouse a week if that is what it will eat.
I would rather actually see a photo of the animal in question before I would say anything about it being underfed.
Many of our animals are fat and overfed.

If you think she was underfed go small and slow on reintroducing food, too much too fast is going to lead to even more issues. One prey item, not multiples.

Id agree with all the above suggestions and add that I wouldn't be too bothered about her being on the small side as youre presumably not going to be breeding her . Just get her healthy if you feel she's underweight .

Sent from my Hudl HT7S3 using Tapatalk

Well your snake must be a survivor. I'm a newb to ball pythons too. Will it grow much if she's already 9?

Sent from my C6743 using Tapatalk