I'm SOO sorry! I know you're exhausted! My son is 18 mo old and went through phases of doing this. For him, his day time naps were too long and were causing a disruption in his night time sleep. I started to limit his morning and afternoon naps to about 1 hr and he went back to STTN. Nap when she naps during the day---you need it, it's ok if your house falls apart. Your husband can pick up the slack. And when he was up in the night, I also started laying on his floor w/a pillow and comforter so I could doze in and out while he did his thing--since he would scream if I left (even though he's been sleep trained for MONTHS). For my son ibuprofen works WAAY better than Tylenol.
And also, sounds like she's transitioning to one nap a day. I have slowly worked my way to a nap around 11:30 (rather than 10am after 6am wake up) and a short crib "rest" around 4. He often won't sleep at 4 but just lays around/hangs out for about 30 min. I need that 2nd break in the day too! We also started to have to go out EVERY day. Usually if we go out around 9-10 for an hour or so this helps him get thru his tired period better (if we don't go out, these tired periods are when the acting out starts) then have a snack when we get home followed by his 1 nap for the day is around 1.5-2 hrs.
Also, the new behavior can be related to her sleeplessness, but it's def not too early for gently discipline. That's exactly the age when my son started! I started telling my son in a very calm but stern voice, "we don't do that, please say sorry". And now, although he will still do things, he clearly knows that they're wrong and says "no, no" (as in "I know I'm not supposed to do this") or "uh oh" after he's done it. All I can ask for at this age is knowing the diff bet right and wrong even if he can't control his impulses. We also do 30 sec time outs after 3 warnings. And he really gets it. He knows what's happening. :)
Best of luck, be gentle with yourself and rest as much as you can. Easy dinners, husband help w/housework, TV help if you need a break--no kid ever became a criminal from an hour of Dora or Curious George! or even a paci all help to keep you sane which makes you a better mom! :)