Now, I normally am very capable of giving people information on what to put in with their bettas. I always give people advice on that sort of thing, most people take my advice. I almost always say "put in fish like bottom feeders that don't get huge" and tell them that aquatic frogs, snails, certain shrimp, are all options. But brightly colored things and things with long flashy fins should be avoided at all costs. HOWEVER, I have a betta in my 20gal with a VERY flashy Copper Marble Balloon molly, another black balloon molly, a silver molly and 2 glass catfish, and NO ONE bothers each other. So, I would hate to suggest that to someone if it doesn't work out. I always tell them it depends on the betta, how aggressive and territorial it is, how they keep their water quality, etc.
She doesn't want to do things like snails and shrimp, and you can't get aquatic frogs in Maine. SO, any more suggestions other than bottom feeders, shrimp, illegal in Maine things and snails?