What do to with this myrrh?

Her most important stat is her defense, so an attack bane isn't really that big of a deal.

And you can always make her a speedy Myrrh.

Hone Dragons'/Hone Fliers' +6 speed buff + Fury 3 puts her at 38 speed. Dark Breath+ refined for speed puts her at 41, and Dark Breath (refined) lowers the enemy's speed, and attack, by 7.

Or you could replace Fury with something else since it lowers her HP every battle.

Best build? Probably not, but it can be loads of fun. :P