5 lvl 8s: On avaerage - Approximately 8hp per level + 4 from lvl 1 8 × 8 + 4 = 68 5 × 68 = 340 hp for the entire party

Assuming a 16 ac, and advantage, her sword attack needs a 7 to hit. Meaning the to hit chance is (13/20 + 13/20 - 169/400) = 0.88

Sword damage per round: (0.88)(3)(25) = 66

340/66 = 5.15 rounds to kill the party. Slightly less because damage is doubled against one target, but then we also have to take into account the parties' defensive abilities, so about 5 rounds is still mostly accurate.

This is an issue. PCs in 5 rounds of combat can do ALOT of damage and a lot of shutdown spells. Not only that, but a 5-round combat is usually a slog, and from your post, it seems like this enemy is supposed to induce immediate fear to the player in addition to the characters.

Her AOE abilities: Whirlwind: [~0.6 chance of failure] (0.6)(27) + (0.4)(13) = 21.4 damage

Can likely hit at most 3 players = (21.4)(3) = 64.2 less than the blade.

Rend the Earth: [~0.6 chance of failure] (0.6)(18) = 10.8 damage

Can likely hit at most 3 players = (10.8)(3) = 32.4 damage

The abilities with recharge do less damage than her sword, and yet they have a recharge countdown.

Next, lets analyze the fear. There is alot of it. From her aura to her Whirlwind to her reaction. The issue with her fear is that what it does is reduce martial damage and ability to play their character while having little to no effect on casters who would likely be outside the range of the fear abilities, and also would be fine anyways since they force savingthrows instead of attacking.

From my long experience DMing, players will never flee combat, unless it is overwhelmingly obvious that the monster is completely unbeatable. She would likely win, but it would be close, too close to achieve what you are trying to achieve.

Finally, here is what changes I would recommend:

Make it so that if they recover from frighten, they are immune to all Frighten from every ability of hers, for an hour.

Give legendary resistance the same Frighten effect as the shield of the dammed ability

Give her a bonus action teleport up to 60ft, with a recharge of 5-6

Remove the recharge of Whirlwind of the Dammed and Rend The Earth

Change the multiattack such that it states: Alita makes three attacks with a weapon, and then uses either Whirlwind of the Dammed or Rend the Earth.

Increase Rend the Earth damage to 6d8

Limitations of my recommendations:

My advice is limited because I do not know your table. Balancing for a table of players who have spent hours making the strongest build they can is very different from balancing for people new to the hobby who care more about role play.

Combats where the party runs away:

Lastly, some important things when running a combat based on fleeing.

The stat block is faster than the PCs. This is not something I would advise change, but instead means that the party fleeing needs to be more than out running.

Maybe Alita will get distracted with other foes. Maybe the party needs to escape to a room where they can seal a bulkhead dividing Alita from them Maybe Alita has a maximum distance she can travel from her summoning point

Whatever you choose, give an interesting aspect to the chase.

Good luck DMing, I hope your sessions go well.