See
this blog and
this.
Only way to kill her with sheer AP is the Earth Destruction Bomb. But that's only when extremely blood-lusted. And nothing suggests he has more than 1 of this. He blows her up, she regens/ resurrects herself, after taking that bomb knew he was dangerous, and hax him to death.
He ain't making her stop attacking him with that mind hax resistance. Probably the same for illusions
Most haxless weapons don't mean jack with that dura + regen + resurrection
Existence Erasure is OoC, and nothing showed it works on an astronomically stronger being.
Force-fields and intangibility meet reality warping and transmutation.
Hax that likely work:
Substitution Gun: If he pulls this out from the start, he likely wins as Wanda will be at the receiving end of her own magic.
Fear Creation Machine only works if you give him her name. But I don't know her response to seeing something she fears, so...
Stop Camera, Pocket Traffic Light, Gorgon Head and Time Stop Watch are a possibility. Not used that often in in-character combat, however.
Combining Voodoo Camera and Bad Luck Diamond so that Wanda's attacks affect her own voodoo doll is a possibility, but it was never shown to redirect magical stuff
Scenario Lighter requires a script written before hand, and that the lighter must be constantly lit
Time Compression Gun is likely, as it has been used a few times in actual combat unlike the stuff above. But idk about aging a 10,000 year old fairy
Transmutation is even less likely to be used than most time hax
Overall, there are haxes that likely work but require prep and knowledge. You give prep and knowledge to both of them though, Wanda likely destroys because most of Doraemon's haxes also had the factor of surprise to succeed most of the time.