I remember your other thread about this issue. Mannequins can't be sold or given to anyone else. Once you get one, you're stuck with it. Gracie normally gives one as a gift with the first purchase you make in her shop. Have you bought another item from her to see if that works?
I love you, Bailey.
12/31/2005 - 02/04/2018
If you didn't save, the game shouldn't have registered that you received the mannequin. In that case, if it's not in the depths of storage, you probably sold it.
The only other thing I can think of is that it's possible she gives you the mannequin at a random time after you accomplish the prerequisites. So maybe she's holding out? But I think that's unlikely, since you receive the other mannequins pretty quickly after you've accomplished the required tasks.