She is cutting her top two teeth at the moment so could this be the culprit?
Yes, definitely. Both my kids, my DD more so (DS just wakes off and on all night long
), have been prone to EWs with teething. It's like they notice they are uncomfortable when they come into that light sleep in the wee hours and then just wake up. I'd rule this out before doing any kind of EASY tweaking. Are you giving meds at all? I've never done it, but I know several ladies here give a dream med, kind of like a dream feed. They go in at around 3/3:30 am and give LO meds without fully waking her up. That way, she hopefully sleeps through that EW. I think it's worth a try.
Routine-wise, you mentioned she's been sleeping through for about a month. Has it been on the routine you posted (starting at 6, of course)? And for the last few days, she's been making it from 5:15 til 9:45 for a nap?