This Theory About "Her" on This Is Us Is a Total Game Changer
This Is Us season three is officially underway, and the premiere only intensified the mystery surrounding the future "her" that Randall and adult Tess are presumably on their way to visit. In the premiere, Randall calls a lonely looking Toby and asks if he's coming down. The implication is that Randall wants Toby to go with him and Tess to see "her." Toby responds that he's not sure she wants to see him, to which Randall tells him "she wants you to be there." The episode hints that the her in question is Kate, but as Reddit user Marty5151 points out, Toby and Randall's conversation sets up the possibility that the "her" on This Is Us is actually two different people. Confused yet? It's OK, we're here to help you make sense of the show's latest mind-bending theory.
Who is the "her" Tess and Randall are going to see? 
OK, so it's clear from the season two finale that Tess and Randall are dreading going to see "her." Originally, this led some fans to speculate that something happens to Beth, Deja, or Annie. Tess specifically tells her father that she's "not ready" to face seeing whoever this person is. Now this could be because the "her" in question is sick or dying, or because she did something to hurt the Pearson family.
In a recent interview with The Wrap, actor Sterling K. Brown explained that Randall is seeking out his family members, and Tess, in particular, to go see this person. He explained, "There's a reason why he had to seek out Tess in particular. Yes, there's a reason why he had to seek out Tess in particular, because Tess hadn't seen the 'her' for some time. And so there's a reason why its time to go and she's like, 'I can't.' There's a reason. Other people may have been more easily galvanized, but Tess needed a little more coaxing."
And yes, the person concerns Toby, as well, even though he's no longer wearing his wedding ring. But that doesn't necessarily mean that the "her" is Kate, or even a single person.
Toby isn't sure Kate wants him there. 
Reddit user Marty5151 suggests that the "her" that Toby is referring to on the phone is most likely Kate. Clearly, something has happened between the two of them — like perhaps a divorce (or worse). If Randall is rallying the entire family, he may believe that Kate will need Toby's support, even though Toby isn't so sure about that. That means that while Randall and Toby are talking about one "her," Randall and Tess could be talking about another person entirely, someone who the entire family is intimately connected to.
Is Rebecca the original "her"? 
Marty5151 posits that This Is Us is planning a major twist that involves the "her" in question being Zoe, who will be responsible for hurting Kevin in a serious way. This would certainly explain why Tess is avoiding seeing this person since she's been shown to be close with her Uncle Kevin. And it would also make sense that Toby would need to be there to support Kate through possibly saying goodbye to Kevin, even if they're separated.
Zoe isn't the only option though. There's an excellent chance that Toby's "her" is Kate, while Randall, Tess, and the rest of the Pearsons are all going to say farewell to Rebecca. It seems odd that Randall is the one rallying everyone together if Rebecca is still alive and well. However, if she's been suffering from a prolonged illness, it would be natural for Tess to be having trouble working up the nerve to visit her grandmother, and it would also be totally normal for Toby to be unsure whether he should go see Rebecca at all if he's on the outs with Kate.
No matter who the original "her" is, there's plenty of evidence to suggest that there are actually two different mystery women now, thanks to Randall and Toby's phone call. It seems clear at this point that one of those women is Kate, but don't be surprised is she's doesn't turn out to be the one that has the entire Pearson clan gathering together.