So sorry to hear all this. Love Pat's suggestions, and hope that Gracie is feel g better this evening. Poor little peanut has been through so much this month. And momma too!
If B12 is cold, can they do what I use to do with insulin? I would load the syringe and hold it under my armpit (cap still on of course, lol), or between my lips to warm it up slightly before injecting.
Personally I would think it would be many weeks that she would have sensitivity along the head, neck and spine areas. Of course, I have no practical experience with this.
Thinking of and praying for you and your sweet Gracie.