It's not 51-49, it's 49-48-3.

[Polybius]

8. One didn't make it too clear

While Sanders and King formally caucus with Democrats, Sinema declined to explicitly say that she would do the same. She did note, however, that she expects to keep her committee assignments – a signal that she doesn’t plan to upend the Senate composition, since Senate Majority Leader Chuck Schumer controls committee rosters for Democrats. “When I come to work each day, it’ll be the same,” Sinema said. “I’m going to still come to work and hopefully serve on the same committees I’ve been serving on and continue to work well with my colleagues at both political parties.”

It would have been nice if she hadn't declined to say it. Of course, you're still right that she will almost certainly still do so.