If it's about toys, that's obviously her collateral. If she can't share them, then she can't have them - take the toys off her. If she wont let her brother play with shared toys in a shared room, then nobody gets to play with them. Honestly, it wont bother him, babies at that age will have just as much fun exploring the shag carpet or chewing on a rusk, but it will have an impact on her.