In the comics, Valeria Richards has quite a convoluted origin story. Before retcons, she was introduced as the daughter of Doctor Doom and Sue Storm from an alternate universe. I feel like that would be the perfect way to add Valeria to the MCU. The Avengers movies could have Valeria be the daughter of Robert Downey Jr.'s Doctor Doom, and after them, when RDJ leaves the MCU for good, perhaps with his Doom dying, she could continue on Earth-616 as part of the Fantastic Four, bonding with this world's Sue and being a sister to the young Franklin Richards.
