Hi there, we were lucky and when F switched to 1 nap he finally napped beautifully. Your LO sounds like she got in a bit of an UT/OT loop there, I would say that you may need to bump up that A time to get a longer nap. F was on a crazy high A time (7 hrs some days!) but he was doing up to 3 hr naps. We moved him to 1 nap at 12 mths. We didn't have a choice on the time because he was in daycare.
Your plan of action on the short nap day is really what you are doing...early bedtime. But when she does a stellar night like she did previously, you can bump up that next morning A time to see if that helps the nap. So from a 6:30 waking, I'd be aiming for a 12 noon or 12:30 pm nap. And you have to stick with it until she gets used to the longer A time, at least 3-5 days. Will she AP a PM cat nap? If so you could do a short 20-30 min PM CN and then put her to bed later than you normally would. That might reset your day.
The thing is, until she gets used to the A times being so high it sometimes takes all this bouncing around between 1 and 2 nap days and EBT. It's a pain with any transition, but particularly with this one.