Wanda was indeed powerful during House of M.. its basically, her words = reality.. but we have to remember one special thing.. Wanda proclaimed "NO MORE MUTANTS".. a spell that was cast upon billions of souls, over worlds, dimensions and realities.. as Beast would put it, that in a moment of mental instability, she uttered three simple words that nearly robbed nearly all mutants on Earth and perhaps the entire omniverse of their powers.. Wanda specifically said no more mutants.. that was why the mutant gene had become inactive and no mutant manifestation occurred again after M-Day.. that was until the Messiah was born.. the Mutant Messiah has proven herself with strong connections with the Phoenix Force.. and the Phoenix itself calling her "my child".. the thing is, despite all of Wanda's powers during House of M, only one force was powerful enough to break her curse over mutant kind.. and that was the Phoenix..