sometimes it will be a case of riding it out. is there anyway that you could bring lunch forward a little bit (for example, there are times when DD was transitioning that she ate lunch earlier like at 11am ish). that way she might be able to sleep say, from 12-2ish ITMS. and bit by bit as she gets used to regulating her new body clock routine of one nap a day you can move lunch to a more conventional time. (for example DD has just turned 2 and her lunch is now at 12.30-1.00pm on an average day) and then goes for her nap at 1.30...

i am confident that she will find her groove going by the fact that she appears to sleep well during the day in the past xx