I think that’s possible. I also think it’s possible that Tink is very tricky and is working many angles.
So my theory goes like this:
–Regina, before she is married to Leo, asks Tink to intercede and get her out of the marriage.
–Tink claims she cannot help but really PP has told her not to because…
–Regina turns to Rumple for help thereby slowly turning her toward power and becoming the evil in order to cast the Curse
–Regina, after she is married, asks Tink to murder Snow White
–Tink “agrees” but really won’t.
–Tink goes to Snow and offers her the bad dust that will help her defeat Regina knowing, becuase PP has the sight, that the dust will really be used to save Charming in 103 thereby sealing the TL of Snowing.
Also I get the feeling that Tink’s banishment has more to do with Blue than Regina. We know that Blue and Tink are going to have some sort of interaction.