I'm pretty new to snakes too and I also have a baby/juvenile Corn who's about 3 months old now. I usually keep my tank around 25-28c (77-79F) on the hot side (sometimes 30 which isn't a problem) and about 22-25c (72-77F) on the cool side, you do not need a heat lamp, a heat mat will do just fine and I strongly advise you get a thermostat to keep temperatures regulated and to keep your tank from getting too hot and the snake being burnt. Now with humidity colubrids such as Corns don't have to be worried about, give them an appropriate sized water dish and they will be fine. What Kera said is right the dial temperature gauges aren't too accurate but they're sufficient enough, if you want to be almost pin point accurate I'd advise maybe investing in a temp gun. Considering that my Corn is only about 3 months old and already a foot I'd imagine your snake will be roughly 3 feet long so I hope you have a large enough enclosure for her. I know your main question was about heat but I just thought I'd be thorough lol

I hope you have lots of fun with your girl!