How else is she acting "strange"? Could overheating be a possibility? My dog does not eat very much at all when she is hot. Take a look at her gums: What color are they? Are they tacky/sticky or smooth? If you think your puppy is sick please take her to the vet.
****I am currently working towards my BSA in Animal Health Technology. However I am NOT a professional. A veterinarian is the only one qualified to diagnose and treat your dog.****
In addition to the important questions asked by tabby823, I am wondering whether your puppy had all her vaccinations? These could be the early symptoms of parvovirus or a number of other possibilities. I do think you need to get your puppy to the vet straight away, as it's better to be safe than sorry with symptoms like this. Tony
No matter what kind of advice you receive here on the forum, it is best for you to take her to the vet to be looked at since we can only guess at what it might be based on the very few details you have provided us with. At six months (approx.) of age it could also be a case of her entering her first heat cycle if she is not already spayed. A lot of females act "off" when they experience their first heat cycle and it's not uncommon for them to skip a meal or two and just lay around a lot acting as if they don't feel well. Is her vulva enlarged at all or is there any type of discharge from it?
Ghilly