Offer to buy her something nice for letting you get the clown knife? Or maybe get a black ghost knife? They are also quite beautiful and move very unusually and gracefully. They are sleek and to me they look like they have a equine head and I have read they can be tamed and will eat from your hand. If you are interested show her a few photos. If she won't go for the gift idea for the clown knife . How about asking for it as an early (only?) Christmas present? Do a (few)designated chores's for her for designated days and time space? Offer to put it in your private space so she won't have to look at it often. Mix in a fish of her preference. As she gradually gets used to it (the clown knife), it may be able to migrate upriver to a more common space. Or suggest you go shopping for his and her fish. Start by going window shopping on the internet? End with a romantic dinner out. Think of some fish that would appeal to her. You already know what you like. Just some suggestions, hope one ( or more) might work.