Would i be correct in saying that she would strongly disapprove of her worshippers cultivating populations for harvest?
This may be a question that's too contingent to answer categorically, depending on the situation she and the worshippers were in, and what/who was being farmed.
The answer may well be completely different if they were to cultivate Eldar or Orks, to take two extreme examples.
Given that this is Warhammer, Isha's orgin as an engineered weapon system, and what Cegorach has some of his agents doing, I wouldn't be surprised if Isha was willing to do pretty much anything that would help her and her children survive.
She's not the god of being a good person, despite some fanon pushing in that direction, she's the god of nature and the harvest. Harvest has some particular implications when you're talking about a species and pantheon literally built for war, given that the Old Ones presumably engineered in the Eldar's capability to eat people's souls and emotions deliberately to make them better soldiers, as they could power up and heal themselves by eating their enemies and any emotions they inspired in either enemies or allies.
Thinking about it, in this setting, where some of the Eldar's original capabilities are actually granted blessings from their gods, I wonder if there's a connection between the Eldar being able to harvest and eat souls and emotions and their Goddess of the Harvest still being alive.
It's quite a powerful inherent supernatural ability, one that not only allows them to power up but also to regenerate from even critical injuries and age as well as super-charge their physical abilities.
If Isha is linked to biomancy that would all make sense. The Dark Eldar would just be pushing their still extant Blessing from Isha to the max, which is why they can do all this without actively drawing on the Warp to fuel a psyker power, indeed when suppressing their psyker talent. Isha's Blessing would be the explanation, allowing them to both harvest the energy and use it to strengthen their living bodies. Notably Craftworld also can access a blessing of Isha that lets them regenerate, although they can no longer do so independently, they need the assistance of a specialist healer to trigger it. That may be part of the same blessing here.
Or maybe not. Just thought that might be an interesting possibility.
If it's true it might make evangelism of Isha worship to the Webway Eldar easier, if we can explain this to them, and say that they are benefiting from her continued existence, and that strengthening her with their worship may directly pay off for them.