Probably not. I think that's just something common to gyaru.
Yua doesn't have one in chapter 1 (p7) or the old photo in chapter 11.5 (p8|184). Reina has one in chapter 1 (p36). I'd guess that Yua saw them on Reina and Yazawa and got hers by chapter 3 (p15). Though, it's too bad we didn't get to...
Does anyone know if this manga will be continued?
It looks like the author hasn't posted on Twitter/X for a year. Has anyone heard anything from elsewhere?
I agree that the tongue piercing has significant history behind it and it's not just an accessory. Too bad we don't (yet) know what that is. (As others have said, it's probably related to some she loved in the past.)