I mean that, depending on Warwick's mental state once he reaches adulthood, Elizabeth may wind up with a lot of power for an English queen.
I expect this is likely even if Warwick isn't incapacitated. Elizabeth will be the senior member of their marriage for years by the time he's an adult; that won't be easy for him to shake as long as she plays it smart (and history indicates that, if nothing else, she could adapt to whichever circumstance she found herself in). One big difference between her and Margaret of Anjou, however, is that she's English. And the daughter of a beloved king. I expect that will get her a lot more leeway than Margaret of Anjou ever got, who was not just a woman, but a foreigner. If Elizabeth is a power behind the throne, people will probably accept it from Edward IV's daughter in a way they would never accept a foreigner "manipulating" their king. She'll get a lot more benefit of the doubt.