The first thing we need to do is to get your pup to vomit up the rest of the teabag she ate. The way to make that happen is pretty easy and instructions can be found here: http://www.petplace.com/dogs/how-to-induce-vomiting-emesis-in-dogs/page1.aspx
Once you've induced vomiting, you'll need to monitor your pup for signs of trouble: Fast heart rate, vomiting, nausea (your dog will most likely lick lips a lot and look like she wants to vomit), increased panting, straining to defecate and/or vomit without any success and increased thirst are all signs that your dog needs to be seen by the nearest emergency clinic.
If you've gotten the teabag out before it's gotten too far into the digestive system, you can most likely just monitor your dog for tonight, but I would absolutely call your regular vet in the morning and see if they think she needs to be seen.
I hope this helps