One possibility is that she could try to find a way to escape from the stranger. Maybe she'll use her wits and look for an opportunity when the stranger is distracted.
She could also leave some sort of clue for others to find. If she's in a place where there are objects she can manipulate, like leaving a mark on the wall or scattering some items in a certain pattern that might be recognizable to someone who comes looking for her. In a more extreme case, if she has a mobile device hidden on her, she could try to use it to call for help without the stranger noticing.
She should stay calm. Panicking will only cloud her judgment. If she can keep her cool, she'll be better able to think clearly and assess the situation.
One possibility is that the Upside Down continues to evolve. New and more terrifying creatures could emerge, forcing the kids (now grown up) to reunite and use their combined skills once again. Maybe Eleven's powers have developed in unexpected ways, allowing her to not only move objects with her mind but also manipulate time or space to some extent.
She could be at a big event like a concert or a fair. There are long lines for the portable toilets. She might be getting more and more desperate as she inches forward in the line, all the while thinking about how much she just needs to go right then. And she might be looking around for any alternative, like a secluded corner, but also being worried about getting in trouble if she's caught.
She might be greeted by a worried or angry spouse. If she's been out for a wild story - related adventure, there could be a big argument about her whereabouts and actions.
Well, there could be a sequel. Maybe new characters will be introduced, or the existing ones will face new challenges. For example, if it's a story about a hero, he might encounter an even stronger villain in the next part.
Maybe there would be a sudden, unexplained noise. Like a loud creaking from an old, abandoned house. The main character might then start to feel as if they're being watched, but when they look around, there's nothing there. Then, they notice a single footprint in the mud that wasn't there before.
One possible motive could be robbery. Maybe he thought the wife had valuable things and took her to force her to give up her valuables.
A wife was in her hottub when she heard a noise. Looking up, she saw a stranger who had accidentally wandered into her yard. He apologized profusely. The wife, feeling a bit uneasy but also realizing it was an honest mistake, told the stranger to leave. After he left, she made sure to lock the gate better and then continued to relax in the hottub, though she was a bit more on edge for the rest of her soak.
She might start looking for a restroom urgently. Maybe she'll ask people around her if they know where the nearest one is.
Maybe he gets into an argument with another patron. The bar could be crowded and someone accidentally bumps into him. He takes it the wrong way and words are exchanged. This could lead to a bit of a scuffle until the bartender steps in to break it up.