Hmm, just though I would add a slightly different point of view.
I never extend naps. If she wakes, she gets up. If the nap is too short, I will fight her for another nap later. I think it is easier to do sleep training when they haven't been to sleep yet, than when they just woke - at this age they are standing there thinking "but I DID go to sleep, what is your problem LADY!".
We use WI/PD/WO. I do not count. I listen. If the yelling starts to get very agitated, or she starts to cry, or it simply goes on for ages (in which case I probably have to pick up her lovie etc off the floor
) I go back in and lay her down and say (the same every single time) "No Zara, it is time to go to sleep now". Then I instantly leave. If she starts to cry while I am leaving, I still leave, but return immediately. If she doesn't cry straight away, I go out, and I listen. We have this now to the point where it is unusual to have to go back in more than once.
I think at this age the absolute most important thing you can do is
1/ Give them a chance to work it out. But listen. You will soon learn when you are needed and when they are just letting off steam, or hoping you will stay but not really needing you. Note here, I always go straight in to a cry, but never straight in to a yell.
2/ Be consistant. Do it the same every time. My lo is teething, I know there is pain. But I give her panadol, then expect the same from her as always. Since I have taken this approach, this is the best we have done sleep wise while teething (still NW, but they were very very short).
HTH.