See how 2 naps goes today. If it seems to help then I would be tempted to do it again for a while. I would be aiming for 5.30/6pm bedtime tonight. I think when they get super OT early bedtime can sometimes backfire which may well be happening here, its as tho' they get too tired to make up for lost sleep at night so only do 11-11.5hrs or less which just keeps pushing the wake up earlier.
I think if it hepls get her caught up on sleep then I would go for it again with the 1 nap. If I remember you where getting 5.30ish wake ups and 2x30min naps before you switched to 1 nap and although it was tough going the 1 nap did start to get longer after a couple of weeks and wake ups started getting later, so we know it can and will work for her on 1 nap and we know 2 naps are no longer the long term answer as they just weren't working.
I know its soooo hard and super frustrating. I really thought L would never nap properly again and would cry almost every day at either nap or bed time or both. Really wish I could be there to give you a huge great hug, put your feet up with a cuppa and look after M for you, but all I can offer is a HUGE CYBER HUG
And if it makes you feel any better at all, rest assured I still don't get it easy with L naps, today she is refusing to go to sleep at all, all I can here is Mummy, mummy, UUUPPPPP!!!!! we will of course have super hyber baby on our hands this afternoon and will get plenty of NW's tonight, so your not alone
now shes saying "norny (naughty) mummy, norny mummy, norny mummy UP!"