Nap time advise please

My little one is just about 6 months old. I’m really trying with a schedule but nap times are so hard lately. She’s fighting me every step of the way and I get so frustrated. I always rock her until she’s pretty much asleep and then put her down. One nap around 10, one around 12:45 and one about 4. She will only nap 45 minutes at a time and now she’s fighting so much I go back and forth for an hour trying to get her to nap. Please tell me what to do and how to do it cuz I feel lost. Thanks mamas!