The correct sentence is:
Keisha always lends a hand when it’s needed; she is the epitome of helpfulness.
Explanation: In this sentence, "epitome" is used correctly to describe Keisha as a typical or ideal example of helpfulness. The other sentences incorrectly use "epitome" as a verb or as an adjective, whereas it should be used as a noun to signify someone or something that is a perfect example of a particular quality.