I'm convinced it was left vague on purpose.
A recurring theme in the show is to hint at potential plot points in the future, while leaving the possibility open that it is just ignored. Dan Harmon has stated before that they don't really plan out the future details well in advance. They leave multiple different options open until the time comes to use a plot point. Then it becomes cannon.
They want us to question if Beth is real or a clone going forward. That said, if Beth is a clone, I don't think we will find out for sure until there is a good reason to reveal that information. They now have another back-pocket dues ex machina where "real" Beth can always come out of nowhere and change any situation.
Rick also makes it pretty clear that the audience wont really be able to tell either. He says "Either way, you chill the f** out" (or something like that); meaning we can't definitively say Beth's new behaviour is from cloning or just a new outlook.
The ambiguity is essentially confirmed to be on purpose around 1:30 in this video from the writers/creators:
(it's an adultswim link, might be region locked, I'm not sure, let me know if if it is).
Also in Season 3 episode 10
Beth has to question this for herself, and it leads to the secondary plot in the episode.