Getting a halflinger fit?

I just found out this year instead of riding Holley I was going to be riding Izzy. Izzy is a cute halflinger but she is also a little bit over weight. I do jumping so I want to make sure I get her into good enough shape to take on the jumps. I'm only planning on jumping her about 2 feet because she is about 16. I did a little bit of free lunging today and I just rode her at a walk a little around the arena. I didn't spend more than a half hour with her. I'm also getting the chance to work with her tomorrow and thursday. And ideas on what I should do with her? Thanks!