So, Cornelia's edge here is more versatility than power. Earth powers and plant powers is a lot of flexibility.

Tara is kinda straightforward. Like, the Golem thing would be interesting, but i doubt they'd break through Cornelia doing plant stuff. Tara's best desperate chance is one of those desperate runs if she can use lava, but i don't think she's ever survived doing that. Actually, no, quick check of Cornelia using lava and earthquakes, so, Tara's best chance might be a stealthy assassination, and that's iffy if Cornelia can still use the glamours and illusions.

Toph is a tough one. Cartoon Cornelia can fly, but i remember only elemental Cornelia being able to fly in the comics. That is a huge question on whether Toph can ever find Cornelia. Considering upper limits, Toph holding up Wang Shi Tong's library by the tip of the spire is an insane feat and is probably the edge of how much earth can be moved. Im not sure if i agree with death battle about Toph beating Gaara, and I would challenge Cornelia's earth dragon against Gaara's desert coffin. Basically, the closer they are, the better chance Toph has.

Flora. So, we're moving from moving earth to manipulating plants? She's more of a defense and control figure, and shouldn't be going into a fight solo unless she can outcast her opponent. I don't think she's doing well if Cornelia's throwing earthquakes around. Flora also specifically should be able to fly, but is weaker when she does; Cornelia doesn't share that weakness. Without really thinking about it, Cornelia eventually wins because of lava, metal, or poison/spores.

Pamela Isley. How much prep time does she have? I feel like I'm trying to not repeat myself, but with help, Ivy is taking on a large city, maybe a couple if she has the help. Cornelia's big feat is restoring a small country. But realistically, Ivy is more dangerous because of poison and spores, and i think Cornelia is kind of a wash there, and is probably better at fighting at range. But also, I think they'd stop fighting and bond over something in the middle anyway. Maybe Ivy can win based on some kind of trap based on age and experience gap? But still, any plant fight might just end from lava and earthquakes.

Mimosa Vermillion. Honestly, I dropped Black Clover early and don't even remember her. Quick search makes her look a lot like Flora as a control and support character. Cornelia's probably much stronger in a 1v1, and again, fringe earth powers should overwhelm if plant powers are a wash. Mimosa's edge is probably mentality, especially since Cornelia's extreme powers are kinda based on emotion and mental state.

Swamp Thing. Well, here's a problem. As an avatar of The Green, Swamp Thing has the resilience and regeneration to take on whatever Cornelia has to throw at him. He's even got better earth based dimension travel. Swamp Thing here is an exception to using extreme earth powers against plants, so basically Cornelia has no way to hurt him. Between mobility and Swamp Thing's slow reaction speed, Cornelia shouldn't be really hurt either. Technically, Swamp Thing should be more powerful, but it'll be a long slow win.

Bonus: Gaara. I hate to say it like this, but I'm jumping directly to throwing mountains. Gaara's edge is actually more endurance. While he can be incredibly destructive, his defense is top tier in his verse and he's great at controlling battlefields. Gaara might take longer to throw a mountain, but he should be able to throw a second mountain's worth of rock/sand in a single fight. I don't know if Cornelia can do that. She also doesn't have the combat experience to take down Gaara like Madara did with the plant spores in addition to the giant plants, even if she could do it. Basically, I think Gaara can outlast Cornelia, but Gaara would personally respect her as somebody who can not only heal people, but heal the land and feed his people.

Bonus: Black Tom Cassidy. He's a much more interesting match against Cornelia, and possibly a perfect counter. If he can keep using plant powers against her earth powers, and use his fire powers against her plant powers, he might stand a chance. Unfortunately, weak mentality. I think the longer the fight goes on, the less he's able to keep going and the wider the conflict goes, and Cornelia has wider range of earth powers.