Here is a summary of how Lena's true identity is revealed over the course of the play:
Lena initially introduces herself as Helen Andrews, a distant relative of the Collyer family who has come to help organize their affairs. However, clues emerge over time that call her true identity into question:
•Lena seems unfamiliar with basic facts about the family's history and lives that a relative would likely know. When Mr. Collyer corrects her on details, she seems confused and flustered.
•Lena only has a single bag with her and few personal belongings, suggesting she may be homeless or transient. She insists that her trunk with the rest of her things will arrive soon but it never does.
•Lena's mannerisms, speech patterns, and even physical traits slowly appear more similar to Lena Collyer, the Collyers' long-lost daughter who left home years ago, rather than a distant relative named Helen Andrews.
•Mr. and Mrs. Collyer begin to sense a familiarity in Lena that reminds them of their daughter, though they cannot fully admit it to themselves at first due to years of grief and uncertainty.
Over time, more and more hints accumulate that all point to Lena actually being their long-lost daughter Lena Collyer, though the truth is not explicitly revealed until the final scene of the play. The gradual reveal through subtle clues and hints builds suspense and drama.