Vhaeraun could work. IDK about Eilistraee though unless they drastically change the criteria for 'recruiting' Minthara. Evil playthrough is the only way to get her so far and has the PC doing some rather heinous stuff, and of course if the player sides with the Druids and/or refugees, she *dies*
Honestly, if the player sides with the goblins as of right now, they'd first have to find a way to squeeze in a redemption arc for the Player character before Minthara, because preaching to Minthara about Eilistraee would ring mighty hollow when standing over the bodies of the Tieflings you slaughtered for her.
Yes it's true. I see an opportunity to make Minthara a cleric of Eilistraee when we saved her life by killing the goblin leaders and taking her prisoner; after, she will communicate with us, and sooner or later we will decide to free her and give her a second chance, after which the arc of redemption will begin
I just don’t see a redemption arc after massacring the Druid grove. If there’s a way to avoid it while still being evil, I see a possibility.
Once you wipe out an entire grove of innocent people, you are at the point of no return. At best, her redemption at that point is sacrificing herself to save future lives. There is no happy ending after the massacre.
Remember though, that both Viconia from BG2 and Nathyrra from Neverwinter, also did really bad things and in the end; Viconia could be still redeemed meanwhile Nathyrra was a good aligned person before the game even started. Aribeth from NWM, who wasn't a drow, but an elf/half-elf, also had a way to redeem herself after the attack on Neverwinter city.
Things work here differently than in real life. Trying to apply our IRL worldview and values there will lead us nowhere, because it's both fantasy world and it's also very heavily based on medieval times.
What Minthara does is no different than what Teutonic Knights were doing IRL for example (attacking pagans), in medieval times such things were seen as normal. Almost every year there was a war and basically until the XX th century armies lived mostly off the land. If all of your food is stolen, survival is not possible. Not to mention how many fights happened when people tried to defend their belongings. It's basicaly copy-pasted here and slightly changed to suit the needs of a fantasy world.
Also until PC approaches Minthara, she is very likely to be stuck in circle of doing evil things, simply because of her past/upbringing/her position. In her current situation, someone from outside has to basically "free her" out of this madness.
Based on her dialogue in the camp, she also doesn't seem like an inherently evil person. Many times through game it's hinted that she does, what she does; because she can't see other way as a realistic choice. That doesn't mean that Minthara did/does those things without feeling bad about it.
An example is given when we mind-read her; she is said to be full of guilt because she had to betray and was betrayed by lovers/family members/friends.
As for Nathyrra, she has for example killed countless innocents according to Neverwinter HOTU plot, yet if she survives the campaign, we're told in the ending that she saved countless lives during the rest of her life. I would say that she did redeem herself. Even just after meeting Seer, she acted really nicely and in a selfless way towards the others, rescuing the drow from the paws of Lolth worshippers.