The Unusual Induction of Wanda Jackson
Regarding the voting issue, the Cleveland Plain Dealer has the story:
In another curious subplot, Jackson is being inducted as an early influence, although she was nominated as a performer on the ballot.
When Jackson didn't receive enough votes to get in as a performer, she was singled out for induction by a committee that handpicks early-influence honorees, said Joel Peresman, president and CEO of the Rock and Roll Hall of Fame Foundation.
Sidemen inductees are selected by a separate committee.
So, presumably if Jackson had received the votes to be inducted as a "Performer," she would have been gone in under that tag. Then they would have either appointed some other early influential artist or simply not use that category this year (which isn't uncommon). As commenter Philip pointed out in the comments, other artists have been nominated as performers and later inducted in other categories (Carole King as a "Non-Performer"; King Curtis as a "Sideman"), but never has it happened in the same year. If Wanda Jackson was going to be inducted whether she won or lost the vote, then why bother taking up that valuable spot on the ballot with her name?
As to whether or not Wanda Jackson belongs in the "Early Influence" category at all, let's look at the Rock and Roll Hall of Fame's description of that award.
Artists whose music predated rock and roll but had an impact on the evolution of rock and roll and inspired rock’s leading artists.Rock and roll's origins can be traced to the years just prior to the time when Jackson's career began in 1954. Wanda Jackson got her start nearly the same time Elvis Presley did, so it is strange that she is considered an "early influence" under the Rock Hall's own definition.