My husband and I have twin two yrear old daughters, and we have the same issue every once in a while. Once they establish the pattern, and know HOW to get you back to the room, they (she) will do it until you break the pattern.
VERY IMPORTANT... be ready! You almost need to meditate before she goes to bed, and tell yourself that you WILL NOT pick her up. Let her know, before bed time, that you will not be taking her out of her room tonight. Tell her that, once she goes to bed, she will stay there. Even though she is too young to understand your words, it will help you to stick to it once she does go to bed.
Be ready for her to start crying when you put her to bed. Tell her you love her, and walk out of the room. Set the timer for five minutes and don't go back until the five minutes is up... plug your ears if you have to. When the time is up, go back, DON'T pick her up out of the crib, let her know, "Mommy's here, but it's sleepy time," tuck her back in, and leave the room (even though she will probably still be crying). Set the timer for five more minutes, and do the same thing (go back, let her know mommy loves her, etc.). She will be able to sense that you are serious about not taking her out of the room as long as you believe it. This time, let her know that, "Mommy won't be back for a while now." And set the timer for ten minutes. After you've done the ten minute routine twice, move on to 15 minutes. The first night, you might have to wait for her to cry it out, but it shouldn't last for longer than 20 minutes. The first night will be VERY draining for you, but it will only get easier. For me, my daughter fell asleep in one hour the first night, twenty minutes the second night, and right away the third night. I hope that this helps... good luck!