About to lose it

I don’t know what to do anymore. I’ve tried everything to get my baby to nap longer than 30 min (max) and she just doesn’t do it. I’m starting to lose my patience. I know she has the ability to sleep longer than 30 minutes because she has done it a few times during the day. At night she sleeps anywhere from 8-12 hours without waking up. She can put herself to sleep. We sleep trained her at 4 months and she knows how to fall asleep independently, so her not being able to connect sleep cycles makes no sense. She sleeps in a crib, with white noise machine, in a sleep sac. We have a nap routine. It lasts like five minutes. I know she’s tired because she falls asleep right away. But she keeps waking up after 15-30 minutes. I’m so frustrated! I can’t get anything done. She takes anywhere from 4-5 naps a day. I can’t even leave the house otherwise she will be overtired for her night sleep and it’s just a mess when she gets overtired. I’m seriously considering hiring a sleep consultant at this point. Yes, she sleeps through the night but this barely napping nonsense is literally making me not want any other kids.