Just got an underweight snake

I just took in a snake that someone was giving away for free, they told me she was probably around a year old but she is skinnier than my pinky. I own several snakes but have never had any that are unhealthy so i'm not really sure what to do to help her gain weight. They told me they feed her 3 pinky mice a week, should i feed her more? And how often? I would really appreciate some help

Do you know how much the snake weighs? Any idea how long it is? Can you post a picture? We can better recommend a feeding plan with this information.

She is 40 grams. I'm not sure how old she is exactly but the people I got her from claim she is around a year old

Can you also provide pictures? If she's just *small*, then you could feed her fuzzies.