Elise Montagne was a Human female who lived on an estate north of the Jedi Enclave on Dantooine during the time of the Jedi Civil War. She developed an unhealthy attraction to her husband's protocol droid C8-42-GE3 after his death, prompting the droid to eventually run away from his home and owner.
Revan first met her on the plains just outside the Jedi Enclave, where she stopped him and begged his help in finding her "companion". Revan eventually discovered that the dear companion she was searching for was in fact a droid, but despite being a little unnerved by her mannerisms he agreed to find it for her.
Revan eventually discovered the run away droid and saved it from a vicious Kath Hound attack, only to discover that it had been intentionally trying to destroy itself. C8-42-GE3 explained to Revan that Elise had become obsessed with him and wanted to treat him like her dead husband, which was making her increasingly isolated and insular.
Concerned for her state of mind—and a little unnerved by her affections — he came to the conclusion that she would only get better if he was no longer there.
Revan refused to destroy the droid and him to return to Elise, saying that it would affect her greatly to lose her droid companion. C8-42 reluctantly complied. Elise was very grateful for the return of her droid and doesn't meet Samnt.
If the player tells Elise that the droid was nowhere to be found, she runs out onto the dangerous plains to find him. This is a definite dark-side-oriented action, and most members of your party will give the player criticism for their actions, except the two droids and Canderous.
In another alternative dark side ending, instead of promising to C8-42 to explain to Elise why he had chosen to be destroyed, Revan tells the droid that he would destroy him and tell Elise that he never found him instead. Shocked at his cruelty, the harmless droid becomes enraged and attacks him, and is easily destroyed. Doing this, however, has no effect on what the player later chooses to tell Elise.
In another alternative ending to the mission, Revan destroyed C8-42 at his request. When Revan returned and relayed to her what had happened she was grief-stricken and ran back to the Jedi Enclave, where ironically she met a man named Samnt, and the two of them became close very quickly. At their last meeting Elise thanked Revan for his help, finally admitting that she had been using her droid as a way to cope with her husband's death. She apologized for the way she had been behaving before, and she and her new man left.
There was initially no canonical establishment on what Revan did with the droid since there are many alternatives in the game. The surname Montagne stands for "Mountain" in French.