Being out on her own, maybe she just ate something HUGE, and she hasn't digested it yet. It really looks like a food lump to me, but that's just my opinion. I'd take her to a vet anyway though, for a fecal culture. She's bound to have parasites from feeding on who knows what. She's so cute though with all her scars and stuff. Looks like she's been through heck and back. I really hope you keep her.