New cat change in behaviour

I adopted a female stray cat (DSH, 2 years) a week ago. She was affectionate, vocal, and somewhat curious when she settled in my place, wasn’t scared or hiding even on the first day. Even the previous rescuer said that she had a sweet and loving personality. We brought her to get her vaccination, deflea and deworming treatment a day after we got her. 2 days later she started acting differently, and throwing up white foam. She stopped eating, drinking, and refused to lay down or sleep. The vet couldn’t find out the cause of her vomiting and change of behaviour, so they gave her an anti-nausea shot which kind of helped. Over the next few days, she slowly started eating again in small amounts, but she is still not going back to her normal self. She didn’t react when I bring her treats or foo (she usually runs to me when I feed her) and often sits at the same spot everyday daydreaming or staring into space. She refuses to play or interact with anything (tried almost every toy) and I’m not sure what I should do? I’m thinking it could be stress from the change in environment or due to the presence of other cats in the house (in other rooms)?