Skillnaden mellan Scarlet Witch och Quicksilver i Onslaught Event

Så jag slutade precis läsa ett skott Onslaught Marvel Universe som kan ses som klimax i hela Onslaught-evenemanget :

However Onslaught was far from defeated, now in a purely psionic form, Onslaught had the power to spread all over the universe. Reed Richards determined that non-mutant vessels could absorb Onslaught's power leaving him open to be destroyed. Mr. Fantastic, Invisible Woman, Thing, Human Torch, Captain America, Iron Man, Giant Man, Wasp, Scarlet Witch, Black Panther, Namor, the Falcon, Hawkeye, Bruce Banner all willingly entered into Onslaught's energy form, and Dr. Doom was forced into it when he tried to capitalize from the power.

Skamlöst kopieras från sammanfattningen på marvel.wikia

Men vad jag inte förstår är varför:

Reed Richards holds back Wolverine and Quicksilver because they are mutants but it is no problem that Scarlet Witch goes? She and Quickie are brother and sister (although this is later retconned I believe) and if one is a mutant, then the other one should be on too?