I would recommend starting with a small cage. Can you buy tupperware bins? I make all my own cages from clear tupperware and just melt holes in them for air flow, something a bit like this:

http://farm3.static.flickr.com/2252/...2eb42de962.jpg

I have a soldering iron i use for that and it makes for the cheapest, easiest cages around. This way, you can build an adult sized cage if you want a nice display when she is older, but not break the bank on it. Just be sure to get a tub that is secure and she's can't push up and out of!

good luck!