Not true, Marvel and Disney have been using her for quite a bit of SOLO merch, but somehow seem to forget she exists in the group merch.
Also Fox doesn’t own her, they were just dicks and stole Quicksilver.
As I said, they have the power to use her in marketing, but it is believed they choose not to because they don’t fully own her. The exception is mostly the merch for adults.
Those Celestial Bodies 