My friend Kay is beautiful but lacks consideration for others.
Literal
Friend [appositive-の] Kay [topic-は] beauty is [but-が], people [toward-に] consideration [subject-が] not-have.
思いやり ('consideration, empathy') is a noun derived from 思いやる ('to think about and feel for others'). 思いやりがない is a blunt assessment — 'has no empathy.' The contrastive が creates a sharp pivot between the positive (beautiful) and the negative (inconsiderate).