- And got the T-shirt
Put the box right by her water bottle, and put her food, hay, and pellets either right by the door, or inside the box.
Be patient. Go over and talk to her often. Leave bits of lettuce, tomato, bell pepper, whatever in front of her. She should warm up when she gets used to her situation with you.
- You can quote me
If food left for her isn't disappearing or her water bottle(s) aren't going down at all, then yes, that's cause for concern.
Guineas that have been stuck in shoebox-sized cages will sometimes just 'freeze' when put into adequate space. As a prey animal it can seem frightening and threatening to them.
All that to say, ditto the advice you have received. I'd keep her separate for right now from your other pig just to monitor her eating, drinking and behavior while she's acclimating to her new home, but keep her in the same room if possible. Being able to see, hear and smell another pig will be very comforting to her.
Your other pig is female, right? I assume you know this, but just because the breeder was dumping her does NOT mean she is incapable of more litters.
Please keep us posted on how she's doing. You most likely saved her life by taking her. Thank you for that.