Hi Christine, (Liana posted as I was, too, she's got great advice!)
Great news on the improved settling! I'm so happy for you! And yay for the great night!!
So, at this house a 50 min nap is OT. But, I've obviously led you on that wrong path before
, so it may not be for Sophie. I think your best bet now is to stick with this A time for several days and see what happens (i.e. will she start to lengthen out). It will be interesting to see how she does today with the little more time. That may help to point you where to go from here. But, it does take awhile for things to stretch out, so you might have to be a little patient. For Claire, it took about 2 weeks. There were some longer naps, some shorter naps, but to get the consistently longer ones, it was 2 weeks. (Then, she started teething and it all went downhill, LOL!)
I think you're right about knowing the OT is creeping in, NWs and EWs, etc. Hopefully, others will have more insight on this. But, with the 12 hour nights, she's doing well, so I'd stick to it.