Attacking the grove gets her, but it costs Wyll, Karlach, and Halsin — knocking her out instead, since Patch 7, gets her without losing anyone.
Spoiler warning: this covers an Act 1 decision and its Act 2 payoff.
There are two ways to add Minthara to the party. The one most guides mention first — siding with the goblins and raiding the Emerald Grove — recruits her but permanently costs you Wyll, Karlach, and the chance to recruit Halsin. The other, knocking her unconscious instead of killing her during the Goblin Camp questline, has recruited her without any of that cost since Patch 7. Which one you can actually use depends on which side of the Act 1 conflict you're already on.
If you follow the Absolute in Baldur's Gate 3 and help Minthara's goblins raid the Emerald Grove, she joins the party once you reach Moonrise Towers in Act 2. This is the straightforward path and it always works, but the price is fixed: razing the grove makes Wyll and Karlach refuse to travel with you for the rest of the game, and it closes off recruiting Halsin entirely. Gale can sometimes be talked into staying if you pass a persuasion roll, but the other two losses are permanent. If you haven't decided which companions you want to keep before reaching the grove, this is the moment that decision stops being reversible — worth reading through what to know before you start if you're still early.
If you're defending the grove — or you just don't want to lose Wyll, Karlach, and Halsin — you can still end up with Minthara by beating her down with non-lethal damage rather than lethal. Turn on the Non-Lethal Attacks passive (it's on the hotbar's Passives menu) before you fight her, whether that's in the Shattered Sanctum or during the grove's defense. Reduce her to zero HP with it active and she goes unconscious instead of dying. She then turns up imprisoned at Moonrise Towers in Act 2, where you free her to recruit her — and because you never sided with the goblins, Wyll, Karlach, and Halsin all stay available.
This method has moved around across patches, so treat the details as current rather than fixed forever:
Even with those fixes, the process is still described as a little finicky: resting too early, before the relevant quest step is actually marked complete, is the most commonly reported way it fails to trigger. If you plan to use this method, finish clearing the Goblin Camp's leaders before you next long rest.
Recruiting Minthara by any method doesn't undo the fact that she's a former Absolute lieutenant with her own arc — in Act 2 she's cast out by the cult that used her and pushes to reclaim her Paladin oath, which shapes a chunk of her personal quest regardless of how she joined you.
If you're playing the Dark Urge origin, the two are unusually well-matched from a writing standpoint — she doesn't recoil from your character's nature the way most companions do, and specific Act 3 dialogue exists for showing her what the Dark Urge has done without losing her approval. That doesn't change either recruitment method above; it's a difference in what she says once she's already in the party, not in how you get her there.
If Wyll and Karlach matter more to your run than Minthara does, the knockout route is the one to use — just don't rest until the Goblin Camp's fights are actually finished. If you've already burned that bridge and razed the grove, you can still read up on what a Karlach ending actually requires in can you save Karlach, since recruiting Minthara the canonical way rules out most of them by taking her out of the party first.