What food are you giving her? If shes playing with it and only eatting a little means she hates what you are giving her. As for weight it's not the low considering a full grown female pit weighs 30 to 60 pounds. My pit is 6 months and shes at 45 pounds. She's on a raw food diet and gets freeze dried treats. She's very picky and her current diet is the only food she will eat. I've been feeding her raw for the last 4 months and she's full of energy and looks great.
Also keep in mind that Pits are thinner and lean. Mine is 6 months old vs my 10 week old chunky american bully you see in the gif I made. I've attached a picture of what an American bully will look like full grown. I think a lot of people mix them up. So if people are comparing an APBT
to an American bully then your pit will look considerably thinner and under weight but they are the weight they need to be. But without a picture I can't give you my opinion. If the vet isn't concerned or think she's under weight I wouldn't worry about it.
I've attached a pic of my black pit when she was 12 weeks laying down on the floor and 16 weeks at the window to see the difference to 6 months like in the gif playing with her step sister and the pic of her with the scarf.
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