I would go for the nap at 12 as planned, and keep your expectations low, plan for the 'worst' yk? I mean be prepared to help resettle the nap if needed and be prepared for a tricky night, OT certainly can happen when you change the routine but it's only going to be a few days really and then she'll likely settle down again. Overall she'll end up better rested.
I'd be tempted today to let her do longer than 2hr nap if she wants it, that makes up for the very early start to the day, so she should still make a 7pm BT. After that it'll be a case of trial and error really. She may do really well on a 2hr nap, 11hr night. Or she might be unable to get longer than a 10 hr night in which case she may well need a longer, 2.5hr nap. If it does turn out she isn't going to give you more than a 10hr night then some decisions need to be made about when you want that 10 hrs to be, later BT or earlyish WU? it's not something you have to decide right now though, just saying there's a chance.
She moved to one nap even earlier than my DS, his longer nights after the transition to one nap didn't last very long either.