I've thought about putting some onion in my mother's flower bed (more for
bug and pest control than anything else), but I've got my own garden to
tend. I did plant marigolds in my "edible" garden, though. They seemed
to have lots of positive things they did for the garden with very little
negative.

Breaking the rules? I guess, if you believe in pure flower and vegetable
gardens. Gardeners for years have planted flowers as companions to
vegetables.

We might still plant onion in the flower garden, if we start getting too
many pests...

I put garlic in my flower beds when they sprout, they help with
aphids, so I guess I forgot to include those.

I've also heard that marigolds are good companions for vegetables.
Plus, they'll attract bees and benificial insects.