Like Melissa said, I'd try having her asleep by 6:45 pm. Do you think she'd take 2 naps if she had only 12 hrs at night? Also, maybe the reason she won't take 2 naps is b/c the first one is too long. Many have to start waking theirs from the AM nap in order to get a PM nap. At around 11 months, DD started refusing the PM nap, so I shortened the first one to 40 min.
It seems like your LO needs much more sleep than mine, but here is what my 12 month old is doing right now. Not sure how much it will help, as they are all different, but I thought you might like to know.
Wake 6:30
Sleep 9:50-10:20 (I wake her so she will take an afternoon nap - on 1 nap, she'd get overtired. In just the past few days I shortened it to 30 min, in order to get her to fall asleep on time in the afternoon.)
Sleep 1:05-2:45
Asleep for the night 7:30
DD's awake times are probably much longer than yours would be too.
Let me know if you need more help. I can find more info for you if you need it.
Brooke