Rosa Parks, I would argue, was limited to a particular sphere of influence (civil rights), whereas the president's wife may have his ear directly, every day of his entire career, in every field, from diplomacy to economic development to national infrastructure to military strategy to civil rights, theoretically.
And then your son is also the president? Talk about power.
How about Rachel Carson or Louisa May Alcott? Sorry if this is off topic, but I find it fascinating how American history is increasingly viewed through the lens of race relations.
Just to be clear, this was a response to the comment.
I do not have any opinion on Barbara Bush in particular other than knowing that she has a lifetime of experience in top American political circles and has been widely respected for that.