Sleep training

Our 5 month old currently does every and anything to fight sleep. Whether its naps or bedtime. She will kick her feet, fight her swaddle, try to arch away from me, and shake her head side to side all while grunting LOUDLY to keep herself awake. We have ruled out any tummy troubles such as gas or reflux... she simply fight sleep like its her day job. Im super guilty of coddling and rocking her to sleep every night and you can tell she definitely has sleep associations. Today i finally just gave up at nap time when i couldnt get her to stop even though her eyes were so heavy she could barely open them... i just laid her in her Rock n play and walked out... AND GO FIGURE, she fell right asleep.....

Previously, the past 3 nights i have attempted sleep training leaving her room at 5 min intervals. I put her in her crib unswaddled and left. She just did not stop freaking out. She normally sleeps in the rock n play and is swaddled, so i tried swaddling her so it wasnt so unfamiliar and she screamed until eventually we ended up rocked to sleep and in our rocker again...

So... should i start back up with sleep training and get her comfortable with putting herself to sleep in her rocker first? Or should i just go cold turkey and put her in her crib and break her sleep associations all at once? She usually nurses before sleep, we have a bedtime routine at 7pm and she naps about 3 times a day for 45-hour each time. Im just extremely lost on how to go about it without fueling her fight against sleep and also not letting her 100% cio. Thanks in advance!