Well you say you've had the snake for 3 years.. so it's more or less full grown then. Adult BPs do well in a 30 gallon long tank (tanks actually aren't the best for keeping snakes in.. but since you want to be able to see the snakes easily they're the cheapest option) bigger cages are actually more stressful than smaller ones.. BPs are shy animals and they like to feel secure.

Try giving her an extra hide.. one for the cool side and one for the warm side. Make sure your temperatures and humidity are correct (82-84 degrees cool side 92-94 warm and 50-60% humidity.. measure with a digital thermometer/hygrometer, not the dial ones, they're junk)

If you can provide a picture of the setup, that'd help us to help you too.

As far as colombian red tails.. if you're getting a baby, you'll want a small cage (like a 10 gallon tank.. or even a 5 if it's a small baby) an adult will need either a 4'x2' or 6'x2' cage depending on it's adult size.

Hope that helps.