Hello again Sandra and thanks for waiting.
I have worked out an answer for you, please read it through and see what you think ...
1. I am quite encouraged for the following reasons :
A. The ASPCA Animal Poison Control Center studies suggest that the lowest documented toxic
studies suggest the lowest documented toxic raisin dose is 0.1 oz/kg and 10 to 12 grapes in a 20 pound dog. Going on this Maya would have to have swallowed around 40 grapes before you would need to be concerned.
You can check this information HERE
B. If she vomited up all the grapes and they where whole and undigested then the chances are you have nothing to worry about as the toxin would not have been in her system long enough to cause any problem. I personally have never know a dog have problems with grape toxicity where vomiting was induced within the first hour or so after ingestion.
2. Grape toxicity is a strange toxin and little understood so at the end of the day you should work with you vet if you want to be 100% sure you are doing the right thing. But from what you have told me so far I would be very surprised if Maya comes to any harm.
I hope I have covered your question fully enough but if you would like further clarification or to talk things over a bit more then I will be on-line for the next hour or so and I will be more than pleased to continue working with you.