Elena entered into the Marie life in the moment when she was fighting with her stepfather about the diamonds which were inheritance by Marie mother. They started the sexual relationship which they were clearly enjoying as they were making out in the shower during the discussion about their plan (where Risa Howard later seemed to join to them). For the all world around them, they pretended to hate each other and behaved unfriendly, especially Marie who was calling Elena repeatedly "bitch" and "slut".
After Jay gave up the inheritance of Marie, the girls celebrated their success by sex in the swimming pool and they continued with secret meetings where they were planning the sell of the diamonds and they were constantly making out. When Elena started to be nervous when their story was questioned by police, Marie calmed her down by seduction and the promise of next sex.
Their partner in conspiracy, Chad Johnson, was terrified by police as well and he stole the diamonds from Marie. They followed him into the wood where Marie killed him. She left Elena there to get rid of the body and went to a buyer to sell the diamonds. Elena was caught by Kristen Richards and Michael Morrison there and she was forced to work for them in conviction of Marie.