So no problems at all after the morning meal just after the evening one?
I don't think its discontinuing the pred but it might have been using the pred triggered this.
She could be stressing due to the remembered discomfort from being in the night time crate.
Maybe swap crate styles in the bedroom - ie plastic if you use wire or vice versa? or what if you tether her in the bedroom instead of crating her?
This is a better site on the pred including side effect info
http://www.petplace.com/article.aspx?id=1553
As your dog was only on it a short time that might have been long enough to trigger an ulcer but not so long she needed to taper off the med.
It could just be stress. I'd expect an ulcer to cause problems more than at one specific time the same with any medication reaction.
So this might be a behavioral anxiety issue.
Dogs really do vomit easily - my theory is this is because they often swallow first and change their minds later - and so vomiting to make herself feel better wouldn't be an unusual anxiety reaction.
You might see if tonight giving her some Tagamet or Pepcid an hour before bedtime helps. You can read about using these here
www.petplace.com/article.aspx?id=1514
www.petplace.com/Articles/artShow.asp?artID=1585
And see if just calming the stomach helps her stop vomiting.
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