I am sorry to hear about your Westie.
My name is Rebecca. I am a veterinarian, and will do my best to help.
There are so many conditions that can cause these symptoms: eating something spoiled or indigestible, pancreatitis, infections, internal diseases ( liver, kidney, etc.).
I am worried she is not drinking or urinating. She may be dehydrated.
If you look at her gums, are they a normal bright pink color?
If you gently pinch some skin over her shoulders and let it go, it should go back into position in less than one second. If it takes longer, she is dehydrated.
I am not seeing responses from you. I hope you can see what I am writing!
The website times this live chat out after 10 minutes, so I will try to connect with you another way if I do not hear from you soon.
If her gums are pink and her skin pinch test is less than one second, she is probably stable for now.
Until you can get her checked by your veterinarian, I would try to get her to take liquids like water or broth.
Yellow vomit is just a sign of vomiting on an empty stomach and is not an unusual finding.
The stiff walk could indicate abdominal pain. Some conditions, like pancreatitis, are very painful.