Well this is puzzling. Nikki has an AP Value for being able to hurt David, who, from what I've seen in the calcs for him, ranges from roughly 85,000 to 239,000 joules.
Webby, does not have a known value.
Attack Potency: Wall level (Kicked a hacky sack through a tree, which was enough to make it collapse on its own, casually overpowered a likely athletic, if not peaked fully grown woman in combat)
Webby has better stamina, & intelligence.
"fight takes place in a neutral area, most likely a park"
You mean like the default Central Park, New York, as per Standard Battle Assumptions?
That said, the neutrality is questionable.
Weaknesses: Can be pretty gullible, can be a bit of an airhead, gradually becomes weaker when not in a nature setting.
Nikki has Animal Manipulation. Feat links on her profile says she's controlled bees & a wolf. She might get tricked out of it, or be too airheaded to try it, but it's still an edge. But if she fights anywhere else, she'll get weaker.
What about Lifting Strength?
Nikki scales to Max, who a calc for says: "111.7404628494 kg of force, That's
Above Average Lifting Strength"
Webby:
Lifting Strength: Above Average Human (Comparable to Dewey, who was seen holding The Jewel of Atlantis)
Anyone know how many kg the Jewel of Atlantis might weigh?
The best thing Webby has going for her is this:
Durability: At least
Wall level, possibly
Building level (Survived an impact plane crash)
Between this & her stamina & intelligence, Webby can probably survive.
As far as I can tell, this is a mostly normal fight -Assuming Webby's AP is close to Nikki's- until the animals break out. Then Webby would probably run because she's smart enough to deal with being outnumbered, & would notice Nikki's extreme attachment to nature; Leading the animal controller away from the animals would probably be a good idea.
(Of course, I don't know Nikki. For all I know, she's more aggressive outside of nature, or if you harm nature. Or maybe she gets saddened & vulnerable if you damage it. It's unclear if staying there or trying to lead her away is optimal, but running away seems more LIKELY.)
So yeah. For now, I think Webby might have this, due to her skill, intelligence & stamina, Mid-High difficulty,
but that's without knowing how she compares to 85,000 to 239,000 joules of AP; If she's much lower, Nikki has a good shot.