you will need about a 3 foot by 3 foot viv
a leopard gecko does not need a viv this large. a 2 x 1 foot viv is the minimum for a single gecko, but bigger is always better. mine is in a 42inch x 21inch viv and has planty of space to move about. for stimulation feed things like crickets or locust which she will have to chase more than mealworms. alos why not try making a fake rock background for her to climb on. im planning one for before the end of the holidays and this should provide more space for the gecko and plenty of excercise opportunities. provide plenty of hides and they will feel more secure and at least in the case of mine be more active.
here is a photo of my cage. it is not very natural looking yet, but you could do a similar size and layout cage with more natural looking hides and substrate.
if you stack carefuly, then you could also make a small rock pile for her to climb on and hide in. the best natural substrate is tiles, and sand is not natural as geckos come from areas of hard solid ground in rocky deserts
