Toys for a mellow puppy?

We just got our 4 month old puppy on Monday. She is very gentle, not nervous, but she is very mild and mellow mannered and just happy to be. She has obviously been through a lot as she is very underweight (she'll be a 60-70 pound dog but is currently 15 pounds). We're having trouble getting her to play with her toys. The only thing she seems to enjoy are the denta bones (for bad breath). Any ideas on what a mellow puppy might like to play with or how we can excite her a bit more?