Thank you for your patience. Your girl's symptoms are definitely rather worrying today, and these could be due to anything from an acute gastroenteritis, intestinal worms or an intestinal foreign body (to name but a few possible causes!). You are going to need to continue to keep a close eye on your girl tonight. If she can't keep water down at all, then there is no doubt she will be quite dehydrated by now. If this is indeed the case, then you are best to get your girl straight down to your local ER vet now if you can. Dehydration is probably the biggest concern here, and if it worsens, it can quickly become life threatening. Your local ER vet will be able to start your girl on some intravenous fluids to help quickly rehydrate her. You can with hold her food until the morning now to give her stomach a rest, but do make sure she has plenty of water available and encourage her to drink.
In the meantime, please keep an eye on your girl's mucus membranes, capillary refill time and respiratory rate as follows (do be careful that your girl doesn't try to bite you):
Mucus membranes - flip her lip and look at the color of her gums. They should maintain a nice salmon pink color. Get her to the emergency Vet if they appear white or very pale pink, or if they are a dark deep red color.
Capillary Refill time - this measures blood perfusion and test this by putting your thumb on her gum to apply pressure. After you release your thumb you will see the gum blanch. Capillary refill time is the amount of time it takes (in seconds) for the gum to return to a healthy pink color from the blanched white color. If 2 seconds or less don't worry - if it is taking significantly more time, again - off to the emergency Vet.
Respiratory Rate - if she is continuously panting or open mouth breathing at all tonight, this is a sign of shock and or pain and a signal for a trip to the emergency Vet.
If any of the parameters above aren't right, of if she can't keep water down at all, you really do need to get her seen right away if you can. It is always better to be safe in these situations with young cats. Your local ER vet can carry out a full physical exam, start her on intravenous fluids, give her an injection to help stop her from vomiting, and carry out a couple of diagnostic tests to try and work out why she might be vomiting. All the best with your girl. I hope all of the above makes sense? If you have more questions or if I can help in any other way, please do not hesitate to ask! If you would like to accept my answer, please press RATE OUR CONVERSATION (I am not compensated in any other way). Bonuses are always welcome. Thanks! I hope to work with you again soon!
PS: If you have additional questions after you rate the question, you are welcome to request me for additional conversations if I am on-line or by beginning your question "Dr. E..." or "Pet-doc..." and others will leave the questions for me.