You need to not let her fall asleep in your arms, but once she starts fussing about sleep, walk her to her OWN BED and lay her down. Dont walk, bounce, swing and all that other jazz. It just gets them more aggitated. Also people assume babies cry for need to be played with, which is wrong, they cry for a need of food, sleep, or discomfort. Babies that age only stay awake about, I dunno, 10 or 15 minutes or so after the feeding and diapering . and then they are ready to go back down to nap. So, as soon as she starts to fuss after her feeding, lay her in her crib..She will continue to cry until she falls asleep. that is normal. let her cry it out.
Once she wakes from a nap,and you feed and diaper her as normal... but then wait an hour or two more for her to "fall" asleep,and she doesnt do it, and then try to pat or bounce or lay her down to get her to sleep, she will be overly exaughsted and she will not be able to calm her nervous system down. Hence she will cry forever. So the key is to get her down before exaustion.
It is not going to be easy to change a habit but you should do it now, because the older they get the harder it is to change it. Keeping a journal of when they wake is a good guide- time can get away from you faster than you realize- it may only seem she has been awake 15 minutes but when you check the log you may realize she has been up an hour or longer! Journals are a godsend.
Again don't wait until she gets exaughsted and passes out in your arms but, as soon as she fusses, probably about10 -20 minutes or so after the feeding, walk her to her room and lay her down. Don't pat her or any of that other jazz. Just let her cry a bit, she will fall asleep.