Concerned about Sister's Behaviour?

I've always considered my young sister a drama queen, a bit of a blame shifter, a bit narcissistic, etc; but lately it's gotten a bit more out of hand. At the moment she wants a site on my father's land, which he said he'd probably give to her for to build a house for herself and her bf (expected to propose). During a talk she had with my dad about the planning permission, she got a bit pushy and he ended up saying like "that will be up to the owner". Now she's pissed and has taken off to his holiday house to sulk. As well as this, he won't be able to give her a site anyway until my mother (who has dementia) passes, as they technically have joint ownership. My dad tried to get power of attorney of the land for himself a few years back when he could see my mother decline, but the lawyer wouldn't approve that my mother understood what she was signing for. Basically my sis now blames my dad for not anticipating this. My dad is now semi-retired and my mom is in a nursing home.

Regarding the holiday house, my dad bought it a few years ago, and my sister been living between there and the main house for the last two years. She mainly uses that house to work from home in, and comes back home for weekends. To say a bit more about the situation, about 6 weeks ago she decided to give my dad an 'early' Christmas present of a holiday to Berlin which her and her auntie (dad's side) planned. She now says she's thinking about cancelling that over this. Now I'm almost certain she won't do this though. She just wants to punish him for the way he's acting about his land.

Anyway, she's not answering his calls and he has made other efforts to contact her with her replying by email to tell him that she "needs space". She then blocked his number. My dad often catches up with my older sister, who talks with both of them. She told him to keep trying to get in contact with her. However my dad found out, through her, that she denied blocking his number and was not happy about being accused of it! She has unblocked him since this but is not answering his calls. Also older sis informed him that she is "hurt that he doesn't seem to care about how" she's doing. He has made many efforts to contact her over the last 5 weeks, and has considered driving down to the house. Yesterday she snuck home to get some stuff of hers at the exact time that she knew he'd be out. She wasn't expecting me to be there and asked why I wasn't at work! I, trying to stay out of things, decided not to say anything about her behaviour. She was there for all of 5 mins and now she gone for God knows how long.

I know she won't cancel the trip because she did a very similar thing last year when she pretended to cancel her 30th birthday party that she had in the family home. To briefly explain that one; my older sis planned on coming to the party, but not to stay overnight because of her kids. This annoyed younger sis as they (her, husband, kids) might've ended up only staying for a few hours and then going home without it really feeling like a party at all. In around the time of younger sis's frustration of this, my dad made a badly timed comment. It was something to the effect of [sister: "now my birthday party is this Saturday night" (for the 2nd or 3rd time) - dad: "really am I invited?"]. She sensed that he didn't care enough and in that moment she said "I'll just forget the entire thing so" and stormed off to his holiday house. A few days later my dad saw a whatsapp message on the group from my brother in law asking younger sis something about the party, so he then knew it wasn't being cancelled at all.

She came home the other day at the exact time she knew my dad wouldn't be there, in order to get some of her stuff. She wasn't expecting me to be there and asked why I wasn't at work! She gone now again for God knows how long. I sense she'll be willing to talk to him again soon as I don't think she can keep this up much longer. Such a talk will involve her having to twist things around a lot, but that'll be considered progress by my dad in comparison to not talking at all. But this is hard to watch. In a few months they'll all be over in Rome, on said trip, acting as if none of this happened.

That's the funny thing about saying "I need space", is that it's up to he to decide for how long. If he showed up at the door of his house after a week, it would probably be a case of "I SAID I needed space". However if he didn't, it would go like this ["why haven't you made any effort to check up on me?" - "you said you needed space" - "that was two weeks ago"]. So she thinks she gets to have it both ways! I do have to admit that I'd love to know what goes on in her head. Does she think she's being unfairly treated, or does she just not give a shit? Or is it a combination of both. She seems to have the ability to become equally as offended as if she was genuinely unfairly treated when she's not. I think she's dangerous. Why? because she can do such things without any consequence. Some people just take the view that women can get a bit hysterical sometimes, and that that's kind of normal, but I'm not so sure?!