She's not even two yet. She's unlikely to listen to you when you tell her not to do stuff. She's WAY more likely to lisen to you if you tell her to DO something.
Try to remember she'd not being destructive. She has not idea what being destructive means. She is playing and having fun. I would doubt she made the link between being smacked and the thing she'd just done wrong. She's too young. She'd more likely to just think she can't do anything.
You will be more preoccupied when a new baby comes. You need to sit down with DP and really, really invest some time and energy into protecting DD from toilets and laundry powder etc. Those things can cause her real harm, if you aren't looking and you already know she's a curious little soul. The time and energy and money will pay off. It's just something that a lot of parents have to do to make things easier for everyone in the long run.
I'm not sure you can 'blame' terrible twos. Children don't just turn two and become terrible.
Perhaps you need to schedule some serious mum and DD time in say, 30 min blocks doing lots of fun things - singing, drawing, play-dough. Then she might be more content to play quietly for 10 mins. Then you can join in and play with her and get her little brain active...and tired out. Then she'll sleep well and you'll get a good decent break.
Involve her in the boring stuff like hanging the washing - she has to pass you a peg. She can watch or 'help' while you peel potatoes. My kids used to crack up at all the silly peeling shapes - i have no idea why! Then you get stuff done - and she gets to be stimulated and spend time with her favourite person.
I don't really leave my kids alone yet - and they are much older than yours. They still require lots of my attention to play and keep occupied. They've never really wanted to play on their own :wall:
No-one's perfect. Just try to go easy on her. She's only so little, you might be expecting too much from her.