Cooper has a swollen eye and nose. he gets into a lot of things. Is it ok to give him Benadryl once to see if this helps solve the problem?

I have a female pit bull terrier (spayed) that is 10 months old. Pearl generally has a great disposition and gets along well with everyone including other dogs. The “problem” is that she is showing less and less interest in her dog food when first provided to her. And it’s the meaty stuff (Alpo cans)! I’m not too worried because she usually eats it eventually but she often will wait hours. Yes, Pearl is spoiled with treats and bits of human food but it seems so odd that she would rather eat whatever we might be having (e.g. a french fry) than this wet, meaty food. She weighs about 55 pounds and gets one 13 oz can in the morning and one in the evening. She also has a constant supply of dry food in a dish but she just picks at that upon occasion. She has a regular place to eat near where we eat and spend most of our time and her Alpo is given to her each time on a new (clean) dinner plate. We have one cat that ends up eating some of the food and Pearl doesn’t seem to mind. In fact, Pearl seems to be more interested in trying to eat the cat’s plain dry food than her own. In short, she seems to like eating most anything except her own dog food. Thoughts?