Pig problems

I wasnt sure where to post this so i decided to put it here. I have a problem with my Guinea Pig, shes really fat. The vet says to cut back on the kebble and feed her more vegtibles. I've been doing that but she always wines thats shes hungry, and i feel sad. I'm starting to worry because when she walks her belly touches the ground. Shes wieghs about 3 and a half pounds. Every now and then she eats pasta and doritoes but thats a once and a while thing. Any one else have wieght problems with there pets?

she looks like this one
http://files.automotiveforums.com/gallery/uploads/82015/gpig1.jpg
but twice as fat as this one
http://files.automotiveforums.com/gallery/uploads/82015/jaco4.jpg

does she walk around or just lay there waiting for you to feed here

maybe if u put something that has taste but is low in fat over the vegitables it'll eat it... just like chicken broth or something... im no vet but its just an idea

We had a over weight hamster when we were kids so we just put it into a ball and let it run around the house all day while we were home it lost alot of weight just running in that thing, sometimes if you leave them in their cage they just sleep all day long and don't move.