Napped, I think your girl is dealing with several problems. As others mentioned, I think stress over a new home and anxiety over losing her companion is just one of the problems. Squirrels can exhibit extreme reactions to stress and have actually been known to die from stress. I would put a blanket over the top of her cage. Leave the front open. This will make her feel more secure and less exposed. It will help her settle a little. She needs a box on the cage so that she can hide away until her stress lessens. You can purchase a small bird nest box or even a small cardboard box with a door cut into it will work. It should have soft fleece or T-shirt material inside so she can burrow under it. Don’t use a towel as they can get entrapped with the loops on the towel. The standing in the corner motionless is certainly related to stress and anxiety.
Another issue is without a doubt calcium deficiency. We see squirrels that are sold in pet stores around the world occasionally. Pet stores can’t sell tree squirrels in the US. Many were raised on a “formula” that isn’t even dairy based. They are extremely calcium deficient or totally lacking in calcium. Just because she doesn’t show the symptoms of MBD doesn’t mean she doesn’t have it. With the diet you mention... fruit and seeds... I would assume that she does have calcium deficiency and start calcium supplements. If she is pregnant it is even more critical that she receives calcium. I’m not sure what is available in your country as far a calcium supplements. Most calcium supplements have Vitamin D. Squirrels do need some Vitamin D but the problem is that Vitamin D in large amounts is toxic to squirrels. You can buy calcium carbonate powder on Amazon. I will get a link to the MBD treatment. Because she isn’t showing symptoms, I would give her dosing based on a small squirrel which is half the dose of an adult squirrel. The easiest way to dose calcium is on a cube of avocado. If she refuses the avocado you will have to syringe feed her the doses. Be careful.... she will bite you very hard. Another method is peanut butter balls. I think reducing her stress will make her more willing to eat. Cover the cage except the front.
https://thesquirrelboard.com/forums/...-MBD-Treatment
I would minimize her environmental stress like noise. It will take time to win her over. Even going slow, she will be afraid for a long time. In her DNA she is a wild animal and she is a captive so her instincts are fear. You probably can win her affection with time but she probably won’t be a cuddly pet like a dog. You will have to accept her on her terms.
Thank you for rescuing her from the pet store. She had little chance of survival there.