Sivir's updated lore text quote changed to "I don't care what face is on your coin, as long as it pays." from "Coin may buy you skill for a day, but never loyalty."
When a coin is minted, at least back in the time of kingdoms and empires, the faces of current rulers were embossed on the surface of coins. This implies Sivir has no loyalties outside of money, and I am not sure it sits well with me if all it takes to bring Sivir to your side in a fight is a bigger paycheck.
I don't get the impression that Sivir has ever developed strong ties with anyone. I've had multiple ideas how her personality was shaped, some notably more tragic than others, but the underlying theme is that she trusts most people to only look out for themselves and will abandon you in times of crisis. I did not have an impression that Sivir had strong ties with her hired hands when she accompanied Cassiopeia to the Lost City, even though they were identified as "her band of sell-swords". It felt more like associates she knew could be trusted if the gold was good enough and would think twice about betraying her.
On an unrelated note, I also thought it quite possible that Sivir helped Ezreal find his little artifact as an attempt to solidify her reputation as a renowned guide through the ruins of Shurima.
You must hate Sivir then, as that has been her thing for a while now. What is the difference between "you cant buy my loyalty" and "if someone offers more than you, I'm going to work for them"? It seems to me to be the same thing, as in both she is not fighting for you, but for your money. And if someone would be a better business prospect, then you are out of luck.
Honestly that was pretty much the way she was depicted so far. She worked for Noxus for a while and only didn't want to participate in the ionia invasion because she knew it would get messy and wasn't worth the risk.
*disclaimer, I've read a total of 0 lore*
Just from playing her in the game...I got the feeling that all she did value was money. Seems like the new lore quote that you mentioned is 100% Sivir to me. Again, just from the idea of her I got while playing.
