If the player chooses to have Serge speak to her late in the game, she joins the party, wanting to observe Serge's strength, and if the player has Kid speak with her reveals she was scientific colleagues with Lucca from "Chrono Trigger".
If the player chooses to have Serge speak to her after the first battle with Lynx, she joins the party, wanting to observe Serge's strength. A letter she gives to Kid, if the player chooses to have Serge revive her late in the game, shows that Luccia was scientific colleagues with Lucca from "Chrono Trigger".