I have some questions for you:
Awaiting your reply.
Did the Benadryl decrease the swelling?
Does her stomach feel tight or distended? Does she seem painful in her abdomen?
When did you give her the Greenie?
Due to her age, I recommend taking her to your veterinarian in the morning if at all possible.
It seems as if she is having an allergic reaction - swollen face, vomiting.
Another causes may be a tooth root abscess (swelling under one or both of the eyes).
The swelling and vomiting may not be related, then I worry about the Greenie not passing and causing a possible obstruction.
Since she is older, she may not be able to recover as quickly as a younger animal. So, keep her quiet tonight. If you want to feed her feed her boiled hamburger and rice - 1/3 cup hamburger to 2/3 cups rice - in multiple small feedings. Offer her plenty of water.
Let me know if I can do anything else to help.