bin, deny all knowledge it ever existed or tell her it was abducted in the night by aliens? or that you've packed it in the night? she'll forget all about it, hopefully by the end of the day. then when you do move & she asks, make a show of rummaging and coming up with a complete blank?
or, tell her you have a perfectly good keyboard which you're attached to & if she keeps the broken one you'd have to sacrifice yours? which would mean stressy mummy as no more chilling on t'internet?