It is never wrong to see a vet when you do not know what is wrong with your pet.
Vomiting bile (the gross yellow stuff) means she is vomiting when her stomach is empty.
She could have slow motility issues which is easily "fixed" with Reglan or Metoclopramide. A vet would be needed for this.
I have known IBD to present as vomiting bile as well So if it continues long term - I would be looking a little deeper for reasons.
Excess acid accumulating in her stomach could also be the culprit. The acid can irritate the stomach, leading to vomiting. Diarrhea could also occur if the irritation spreads throughout her system. Pepcid AC could help for acid. I would consult a vet before trying.
Another option would be to try and feed her a bit more then just a snack at bed time. Since she is a bit chubby I would just take a handful of her breakfast, another from her dinner and feed this to her at bedtime (since you are still feeding her the normal amount -just made into three meals - she should not gain weight). See how that works.
Also, you may want to consider gradually switching her diet. There is always the chance that the diet you are currently using simply does not agree. Therefore, changing foods (perhaps to a highly digestible ?sensitive stomach? formula) may have an impact on the problem. Even if your food is the best of the best does not mean it is the best for Tosca.
Good luck.
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