I would do the same thing the vayne did, in the least to earn assists, if not kills. If the choice was between you getting two solo kills, or Vayne getting two kills and you getting assists, I'd take the latter every time as it's more overall team gold. Pushing a Vayne ahead by two kills is pretty huge.
The difference between two solo kills, and two kills with assists is 300g. That's a 3rd kills worth of gold that wouldn't be there otherwise. So 600g to just ekko, or 300g split to all who assisted and 600g to Vayne. It's clear which one is better. Her flash potentially earned the team an extra 300g (I'm still assuming they would have been solo kills without the flash).
Assuming the support was there, you earned 150g from assists, 100g from global tower gold, ~83g from being there when it's destroyed (assuming you, adc, and sup are all there when it goes down), 25g for the global part of tower first blood, and ~91g for local shared from tower first blood.
That's 449g from just assists and towers. You state you lost a wave for the tp to help. Average early cs are worth about 17-18g. For ease of numbers I'll use a flat 20g per cs. That's 120g you lost tp'ing bot. Though it's prob more like 2 waves, that's still 240g (prob like 220-225 since I was rounding up).
You earned a minimum of 450g in this situation. And that's in the worst case scenario. If the sup got no kill or tower assists, then you earned a lot more. An extra 150g from the assists, and an extra 78g from towers, for a possible ~675g. And that's before even taking any cs to just get to tower to destroy it. With cs you could be over 800g, or at least 600g if sup was there.
Vayne's attitude was incorrect, but don't act like a victim when your 1-2 wave loss earned you 200-400g MORE than your waves would have earned (449 worst case scenario gold minus 225g from two waves would be an extra 224g not including any cs). You already earned way more gold than staying in lane, and are wanting to take a from the most gold dependent position.
Her reasoning is correct, her attitude and wording are VERY lacking. You earned a net income with all of that, and put the opposing bot lane way behind. Let your gold dependent adc farm the cs, and accept that you earned200g more than your cs instead of 300g.