We brought home a 1.5 yr old siamese cat, Sheba, 4 days ago. We already have a 10 month old kitten, Gabby. Sheba's been vomiting a clear pinkish liquid every 3 hours. It smells horrible. None of my plants have been eaten which I know can cause them to be sick. She's been getting the same food as before she came to us. And the two cats have been tolerating each other, for the most part.
Any ideas?

Really, only a vet will be of any help.
It could be nothing. Sometimes when animals get stressed their natural immune system goes down, allowing their natural bacteria to take over, giving them a stomach bug. These are easily repaired. However it could also be much more serious so I'd go to the vet asap, if you haven't already.