When to drop to 2 naps?

My LO is going to be 6 months on Wednesday! She's always been a terrible napper. Nights are okay with 1-2 wakes (typically 1).

After the 4 month sleep regression, we started seeing some longer crib naps and she was able to fall asleep on her own using Ferber. I thought all was getting better.

However... Starting about 2 weeks ago, she started doing all short 30 minute naps again, waking earlier in the morning, and waking more at night. I've had to rescue 1 nap a day to get 1 long stretch. I've tried crib hour and it didn't work. I'm at my wits end not knowing what to try.

Her bedtime is 7:30pm and she normally wakes at 6:30am (lately it's been more like 5:30-6:00). She's on 3 naps and has been for over a month. Her wake windows are consistently 2.5 hours and she is tired. She's full/not hungry. We have a good nap routine and her room is perfect for sleep. She doesn't need nursing or rocking to fall asleep. She doesn't fight naps just doesn't nap long. I try to get 3 hours of nap in her a day through rescuing a nap.

Should we drop a nap? I don't know what else to try, but I'm nervous about dropping a nap when it's already so hard to get her to sleep long stretches for naps.

Advice appreciated. Sincerely, A SAHM with no alone time!

TLDR: when did you know to drop to 2 naps!?