Welcome to the forum and the wonderful world of snake keeping, granted it wasn't your choice. I commend you for putting in the effort to provide the snake with a good home.
tttaylorrr is spot on, and one of the forum's best members for helping newbies and experienced keepers alik, so you're in good hands. Like she said, read up on the husbandry stickies she linked and go from there.
It sounds to me like you're really close. My guess is you need to up the strength of your bulb to probably a 100 watt. I use the dark purple ones because I can let them run all night and it remains dark in the enclosure. During the day, the lighting from the windows in the room are plenty for a BP.
Your UTH is there solely to provide a hot spot to aid in digestion and not for ambient temps.
VERY IMPORTANT: ALL heat sources should be regulated by a thermostat to prevent dangerous heat spikes which can cause serious burns or worse to your snake.
As for tank size, yeah, you'll need to upgrade, especially for a female. If you're going to stick with glass a 40 gallon breeder tank is ideal due to its floor space.
We're here to help, so feel free to ask away.
And I don't suspect anybody will be hard on you, you're stepping up and providing a good home for the snake rather than letting it suffer or just dumping it off on Craigslist or something. So, good on you!!