Wanda has almost NO training in magic. She trained with Agatha Harkness for only about six issues. Strange and Mordo spent YEARS studying with the Anicent One. Clea was Strange's disciple for about a decade of issues. Jennifer Kale studied under Dakimh for years. Wanda simply doesn't have the required knowledge.
You're absolutely right on the training thing, indeed, the whole point Strange was making during Disassembled was that she was wielding a power level she had never trained for or earned, and thus couldn't control, but perhaps more importantly, Strange may not be the Sorceror Supreme right now, but eventually, inevitably, the status quo will reset to it being him, and anyone else who takes up the role will be required to crash and burn, usually either in failure or in madness, forcing Strange to return and take the job back.
Look at all the times there's been a new Captain America/Iron Man/Thor or Batman, and how the story always ends with the original coming back. That Strange is a lower-profile character than them (and at this point, arguably lower-profile than the Scarlet Witch) who can't hold his own ongoing book anymore is unlikely to change this Law of Comics from being applied once again.
All that said, if they wanted to try giving her a series, or miniseries, (or, best of all, something teaming her with Vision, Quicksilver and Crystal) it would be a change from the repeated attempts to give Hawkeye/Ms Marvel/Moon Knight a solo book because this time it'll sell