Hi there,
I've done both PUPD (5 mo) and WIWO (19 mo) with my DD and have really liked both methods. I agree with Lizzie, if you think it's some type of SA, you might want to try GW, but since your DD is already an independent sleeper, and it seems like she just wants to go back out with you, the method you're using will probably work well.
A couple things to think about: if this is a new routine and you've cut out the rocking, it may be that she is just looking for that extra cuddle you used to have. Even though you are doing the bottle now downstairs, do you still do a little cuddle, read a book, or sing or pray before placing her in her crib? That may help. Also, if she's never been left to cry, even 2 min is pretty long in her mind. If it's not a mantra cry, you need to go back in sooner than that. I would count to 20 or 30 and if DD was still crying, I'd go back in, say my phrase (I didn't do the put down part at 19 mo because it just made her more mad), leave and start counting again until I heard her switch to a mantra cry. If she switched to a mantra or stopped for just a few seconds, I started my count again.
I noticed (and it's still the same to this day) the more I stayed consistent with it the better. If I leave her for any amount of time and then go back, she continues to put up a fight, because I think she's wondering when I'll come back next. But, if I'm consistent, and just keep up with the monotony of telling her to lie down and go to sleep, she realizes that's all she's going to get and goes down much quicker.
I think since she's been an independent sleeper already, if you're consistent with it, she will go back quickly. I think for my DD it only took a night or two of WIWO for her to go back to just blowing me a kiss goodnight.