Hello, I'm Dr. Kara. I have over 20 years of experience as a veterinarian and I'd like to help with your concerns about Foxie getting stung by a bee.
I am very glad to hear that she received Benadryl immediately as that antihistamine is quite good at stopping allergic reactions. You do want to continue dosing her at 1mg per pound of body weight every 8 hours for at least 72 hours to give the allergen time to clear from her system. If you stop too soon the reaction can flare. The dose you gave (3/4 of a 25mg tablet) is a good one for a 15 to 20 pound dog. Do expect her to be sleepy with that medication so keep her away from stairs so she doesn't fall and hurt herself.
Unfortunately Benadryl doesn't do anything for pain and even with Benadryl we can still see localized swelling at the site of the sting.
As long as her color remains nice and pink, she doesn't have any facial, throat or tongue swelling, she is breathing easily and you aren't seeing any vomiting or diarrhea then her reaction isn't likely life threatening. It is likely just very uncomfortable. The fact that she is sleeping now is a very good sign. That probably means the discomfort isn't horrible. If it were I would expect her to be pawing at her face or rubbing her muzzle on things.
I don't think you have to have her seen tonight given your description of the way she is behaving and the way that you handled things for her. But it certainly never hurts to have her checked and make sure all is well. Your local emergency veterinarian can give her a steroid or a nonsteroidal anti-inflammatory injection and prescribe pain medication for her. Or you can choose to watch her tonight and if she still seems uncomfortable tomorrow you can have her regular veterinarian take a look at her and prescribe medication for her.
In the meantime I do recommend feeding soft foods mixed with water to make eating and swallowing more comfortable.
If she is refusing to eat even soft foods you can try offering meat baby foods
or a bland diet of 1/3 boiled, shredded white chicken and 2/3 boiled white rice. You can mix in low salt chicken broth or water to make the food softer and easier to eat and swallow.
Best of luck with your girl, please let me know if you have any further questions.