Thank you for the replies.
She is a fair size girl and is already in a viv of the same size, so I am sure she will be fine. He sister - kept by the owner is also a big girl too, so must be genetic!
I can't put any vents in the top, as the bulbs are screwed in with a cage attached to it.
I have decided to put a large vent in each side - one at the bottom and the other side at the top for maximum air flow.
That'll keep her happy and warm and moist..... I hope!