Taffy in her playpen

I always put Taffy in her playpen when I clean out her normal cage. I hide food all around in different areas so she can go look for it. This is the only exercise Taffy gets. Otherwise she is very lazy. She was very overweight when we purchased her and I think she may have lost a little bit of weight but not alot. We try to keep her active but there is not alot you can do with a guinea pig.