Whitney Frost was already in the MCU in Agent Carter. If they are doing Madame Masque on this show, it will either be a descendant or somebody else under the mask.
Normally, I would consider the pre-Disney+ Marvel show and movies as separate but Agent Carter is the only show they've bothered to acknowledge in the movies (Jarvis' 5 second cameo in Endgame and the writers saying they accounted for S1 and S2 of the show when they figured out which year Cap reunited with Peggy) but if they are doing MM in the show, there is more chance of a callback to Agent Carter than not.
I'm positive Agent Carter is canon, but as Frontier said, that wasn't Giulietta Nefaria. But maybe they're connected
Masque is almost definitely spoilers:end of spoilers
Kate's mom. You don't get an Oscar nominee be like Vera Farmiga for a small "mom" role
Isn't that similar to the logic people used when they said that Emma Caulfield ("Dottie"/Sarah Proctor) had to be playing more than just a citizen of Westview? Pretty sure during the run people kept saying that there was no way the MCU would hire Emma Caulfield just for bit part, and there's how Agents of SHIELD had Lucy Lawless's character die in the first episode of season 2 and only other appearance be in a flashback.