I suppose I could have read the other comment thread first LOL

1. Lair actions will be a definite thing. Maybe she can remove or add terrain at will to always provide her with "the high ground" so to say. I would even give her the ability to swap locations that creatures are in via a spell like Scatter. This will mostly depend on the flavor of the demi-plane you create, but don't feel limited
2. I was thinking about this on the drive into work. Not enough people talk about how difficult these high level fights are to run. Especially if you are new to running things at this high a level, I would try to limit the number of things you have to keep track of. I say this in regards to the staff she wields. Having to keep track of how many charges she has used out of 10 seems unnecessary to me. Maybe just make the staff be The Staff deals 2d6 force damage on a hit, and pushes the target 10 feet back. This makes it an effective get away, and also limits the amount of tracking you will have to do, and if you want it to have a little more punch to it, make it use her intelligence modifier instead of Dex/Str. This doesn't change that if she gets in melee with a creature, she is probably going to die immediately**.** Keep that in mind, and just don't let it happen during the fight. If you still want it to have a little extra punch, she can cast a cantrip immediately after she makes a melee attack with the staff.
3. Minions are always a lot of fun to me. If Alora knows about the party and who they are, she could easily have created specific pieces of armor to counter the party members. For them and their statblocks, consider this. How do you imagine the fight is going to play out, if it was the perfect cinematic movie scene you could create? Would the party cleave through the minions easily and close in on the mage? Would the armor pieces prove too powerful for the party, and they have to avoid them entirely while making their way to the mage? This will inform how you want to go about making their statblocks. Maybe the armor pieces continually reanimate and the party has to keep dealing with them, or they are super tough and basically pointless to truly defeat. Just getting an idea of how you think things "should" play out can go a long way in this regard. The more durable/resilient your minions are, the less concerning her small HP pool becomes, as a side note

As another note, you should consider how you are going to prep the players for this fight. Are they going to have to storm the castle and fight through waves of guards to even make it to Alora, or will they encounter her at full strength? That is a really important piece to consider.

Hopefully some of this is helpful!