Lady Waltham is a former antagonist in The Legend of Tarzan. She is an aristocratic lady and the sister of the deceased Clayton who wants revenge on Tarzan for killing her brother - at least, in her own mind.
She had her valet Hobson capture those close to Tarzan and she then poisoned him. Tarzan was then given a challenge by Lady Waltham which was either save those he is close to from danger or head to a mountain she dubbed "Clayton's Peak" where the antidote is. Though Tarzan managed to save his friends and family, he then ended up saving Lady Waltham from the leopards Nuru & Sheeta. Afterwards, she gave Tarzan the antidote knowing that Tarzan didn't "kill" her brother.
It is unknown what happened to Lady Waltham afterwards, though it may be presumed that she left the jungle with Hobson to continue on with her life.