Thanks for the question.
Bell peppers are pretty safe for dogs to eat. They don't pose any risk of toxicity or poisoning.
I will qualify this by reminding you that any kind of food ingested that is not normally in the diet has the risk of causing vomiting and diarrhea. I think it would take a fairly big chunk of green pepper to make most dogs sick - but you know your dog better than anyone. If you know she has a sensitive stomach (easily gets vomiting or diarrhea) then you may want to be on the lookout for that.
I hope this answers your question.