I do think dd1 possibly has some difficulties with comprehension and understanding; you tell her not to do something and she does it. Not seemingly to be wilfully disobedient but more doesn’t seem to understand that if she does X then Y will happen.
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It doesn’t matter how many times she’s told what to do, how dangerous it is, she still does it, same with ‘don’t show dd2 your new toy as she’ll take it off you.’ I will come back from a party with dd1 and clearly tell her to go and put the party bag straight in her room and she’ll literally go and show dd2.
FWIW, this (and the exchange where she sounded like she understood why not to pull hair and then immediately did it anyway) is VERY much like DS2 who is nearly 8 now, he's getting there with some things now but if I think back to 2 years ago it's almost spot on to how his behaviour was then, and I think nearly 6 was when I was really starting to find it very very clear that there was a difference between him and other children his age. It's completely baffling because you do expect them to understand at this age. Anyway he is now diagnosed ADHD, suspected ASD. I am not sure whether it was an impulse control thing, like he understood, but he doesn't seem to have the "brakes" which lets him stop and consider whether an action is sensible or what the consequences might be, it's like as soon as the thought enters his head he immediately does it, with absolutely no filter from brain to action, or whether it was that he has communication difficulties, because there are some general oddities here e.g. he quite frequently has arguments over me saying a sentence which means the exact same as a sentence he said but he thinks they are different, he struggles with comprehension reading tasks at school and simple riddles, still finds it vv difficult to distinguish sarcasm, jokes, and pretend games, or will misremember jokes and not realise (e.g. Why did the skeletons not fight? Because they didn't have any guns! - guts - the punchline is guts. But he didn't register that it wasn't funny when misremembered, because he doesn't really understand what's funny about the actual punchline.)
But even e.g. the other day, he found a sharpie pen from somewhere. When he was younger I would have immediately taken it off him but I thought he should be OK, so I just told him to be careful with it because it's permanent so he must only draw on paper with it and he said OK. DH apparently also saw him with it and said something to the same effect. 2-3 mins later DS2 appears showing me the drawings he's done on his nails and then says "Mummy..... you have to promise not to be mad." 
OK..... what? He holds my hand and leads me to a part of the expensive LVP (rented!) floor where he's done a whole little fucking picture of a house and an entire sentence of writing. I lost it immediately and shouted "DS2!!!!!! What on EARTH did you do that for?!?!?!?!" while he looked baffled and wailed "But you promised you wouldn't be mad!!" FFS... anyway luckily it was quick enough that it came off straight away with an alcohol spray. I took some deep breaths and asked him in a calm but clearly narked tone whether he had done any drawings anywhere else and he sheepishly admitted to having drawn on a door frame, the stairs, a glass window and a chair. He claims "I didn't know what permanent means!" Yes but you know what "only draw on paper means" ..... anyway. Luckily all came off but my heart was going at about 1000bpm for a minute or two.
We had all child locks on all car doors obsessively until about a month ago because we'd had incidents where he would just randomly open the car door at a completely unsafe time, including once when we were driving at 70mph on a motorway (and it was a sliding door!) Oh and last year, this led to them accidentally locking themselves into the car, upon which DS2 (then age 6.5) immediately panicked and started crying, and DS3 (then age 3.5) apparently thought about it for a few moments, then climbed into the front to let them out.
DS3 is now nearly 5, and although in many ways he can be a little terror (bolts, takes his clothes off the minute you look away, can be a complete wind up merchant) I am frequently surprised by how good his self-control is, and how much he can listen to instructions when he wants to. With the kinds of examples you give that your DD2 cannot do, DS3 could do these things, and he is not quite 5. There are times that he is naughty or wilfully disobeys of course, but he responds to being told off and it will generally reduce the chance of the behaviour happening again. Completely different to DS2 (and DS1) and hence even though he's quite an active child, I don't think he has ADHD. But there was also a particularly tricky period when he was 3ish where I think he was reacting/copying a lot of the behaviour DS2 had which he couldn't easily control.