The matchup itself is already bad enough for you and Vayne. Sona is one of the better off-counters to Janna because Sona doesn't really have much engage, therefore making disengage kind of pointless. Both she and Jhin easily outtrades you and Vayne at any given time in lane (don't forget heals, people always underestimate the amount of healing Sona could do), and can easily zone the crap out of you two. Yes, even post-level 6 because Vayne can attempt to go all-in for kills, and then gets shredded halfway, and you don't know what kind of buttons to press because it's pretty much a pokefest.
Best bet, play super safe, ask for jungler assistance (they are very easy to gank, let alone a Sona), and just make sure Vayne get as much farm as possible. If Jhin or Sona is looking like they're gonna try to chunk down someone's HP bars, prepare your shield and try to predict who they're gonna attack; it's usually the ADC but smarter ones can rotate between you and her. Get coin because you are not going to do any poking, unless you really want that spooky ghost active afterwards. If Vayne can farm up to Jhin's CS, then you have done your job; their point of "poke lane bully" is pointless.
Focus more on teamfights or even splitpushing, if anything.
EDIT: I forgot something. This is already happening with a Lucian, who is supposed to be a lane bully and can trade early on with most ADCs. Vayne just made the situation more extreme.