Actually a three some could maybe fix this if 1. Anna is able and willing to accept Lily the way she is and if 2. the Duchess and Anna both doesn't mind sharing Lily. But the Duchess is already giving off the vibe that she's too good to share a lover with a lowly servant girl so you maybe right ╮( ̄▽ ̄)╭
Accept her for being dense and easy. Reread chapter 1, she said outright she would rather be the redheads personal toy than to live in her house and be useless. She said that shit directly to Anna, so now that she lives with the redhead it's not surprising that she'll let the redhead have her way with her.

Uffff the girl lily has no spine ,some one comes fucks and again she is being kissed in front of her crush ,like dude how can any human being this naive it's frustrating,even a 3some can't fix this