I ask this to the entire thread.
No, I think it's more that the writers seem to have no idea what to do with her when she's not making those comments. The main thing she does of significance (outside of the Saihorn racing, which I think they are dropping completely) is to have random 10 second hints about how much she likes Ash. It's not even as overt as Takeshi's crushes on every woman ever or Citron's science thing, so I don't feel like it really consumes her character...because she doesn't seem to have much of one in the first place. I feel like Eureka has more significance and personality than Serena so far, and she's not even old enough to be a proper trainer.
I fully agree with Lizardo's comments - even Takeshi seemed to do more than her, and at least he had some sort of goal. I hope they can come up with something for Serena. Maybe the PokeVision episode will come up with something.