Just a thought experiment but - after my pull, where I got 2 golds I got 22 Rainbow Shards for Promoting a girl.
That would imlpy that you get 11 shards per a Gold character pulled.

Or is the amount of Rainbow shards static, and you get it simply for pulling ? (a 11 pulls would give more in that case of course).
That would mean 2 shards per girl pulled, regardless of rarity.