Thing is though, Sunny was more passive than she initially appeared herself. Because for all the perception about her being a trailblazer in attempting to reestablish pony relations, she’s not actually the one who did the trailblazing. She had an open mind, yeah, but she wasn’t the one who actually went out of her way to leave Maretime Bay and make friends with the other races she was so sure would not be hostile. Instead, she waited until a unicorn first waltzed its way into town before she so much as even considered leaving. Evidently, had that never happened, she would have gone the way of her father and went to her grave without ever proving or disproving her beliefs, unless on the off chance she finally managed to change the town’s mind.
So honestly, Izzy is the one who deserves the credit for making the bold move to venture into a town where she likely knew she would not be welcome. For being the first pony in who knows how long that decided to actively seek out the other races. And even if you say that Sunny’s note is what encouraged her in the first place, it doesn’t change the fact that she’s still the one who took that bold first step where Sunny did not. So Sunny was definitely not that proactive when you think about it.