I went straight to a 20g tank and mine was about the same size when i got her. The important thing is to make sure she has a good secure hide.

For the longest time, mine loved this log that to me looked almost flat, but there was just enough room under it for her to squeeze under. She loved that, so it was kind of sad when she out grew it and I had to replace it. She went roaming all over until I finally found a new hide she liked.

Snakes that don't feel secure will roam a lot and usually won't eat. Exploring isn't always good.