Certain aspects of this post worry me. Cats do NOT 'hold grudges' against others - they just don't think that way. I don't believe they get jealous in the way that humans do either, although they can feel pushed out or threatened by a new arrival.
Also, please remember that purring doesn't always mean a cat is happy. A cat who is scared or feels sick may well purr to comfort themselves. That is most likely why Boo's purring when burritoed for meds.
I'm glad the meds are working on the nausea, but please do take things slowly with Boo. I really think she's feeling overwhelmed right now - whether or not the vomiting was cased by stress or something else. Let her chill without any extra pressures for now. She needs some time to decompress and get well.
Also, please remember that purring doesn't always mean a cat is happy. A cat who is scared or feels sick may well purr to comfort themselves. That is most likely why Boo's purring when burritoed for meds.
I'm glad the meds are working on the nausea, but please do take things slowly with Boo. I really think she's feeling overwhelmed right now - whether or not the vomiting was cased by stress or something else. Let her chill without any extra pressures for now. She needs some time to decompress and get well.