Marissa begins assisting lawyer Liza Colby, who is representing Kendall Hart in her trial for murdering Stuart Chandler.

When Stuart's wife Marian Chandler breaks down, she attempts to shoot Kendall in court, but accidentally hits Marissa instead.

When JR learns that he has a rare form of lymphoma, he decides not to tell Marissa, and instead confides in his former step-father Tad Martin.

On November 29, 2010, David attacks Ryan Lavery with the intent to kill him and kidnap Greenlee, whom he had recently married, only to be shot and rendered comatose by Kendall (though the public believes it was in fact Erica).

When he awakens on January 17, 2011, Marissa offers to be his defense attorney and hopefully get him to turn over a new leaf, but assures her father that if he doesn't do exactly as she says, she will see to it personally that he is thrown in prison.

Eventually, Erica manages to convince the governor to grant David a pardon for his crimes after he helps Griffin Castillo perform emergency heart surgery on Kendall.

Infuriated and hurt, Marissa gives up on David completely, but nonetheless makes him tell Ryan where Annie has escaped to.

However, when Reese's lawyer and nanny arrive from Paris to take Miranda and Gabrielle for a visit, Marissa quickly goes to Erica and Jack for help and gets them to back off.

After being repeatedly asked by JR to move back into the mansion, Marissa begins to fear that she is being unreasonable or unfair to AJ, but Kendall and Bianca assure her otherwise.

Bianca reveals to Marissa that Ricky is actually a criminal who is directly responsible for the death of Kendall's husband, Zach Slater.

On August 16, Marissa and Bianca make love for the first time, unbeknownst to them JR secretly taped their sexual encounter and planned to use it to get full custody.

On August 22, Marissa meets AJ's grandmother Dixie Cooney, when she comes to inform Tad that JR had attempted to bribe the presiding judge in their custody hearing with the videotape.

JR handed the video over to Marissa after her and Bianca confronted him over it, but he continued to threaten them and he repeatedly violated the restraining order in one case at a party at Zach and Kendall's home and tried to kidnap AJ.

On the May 2, 2013 episode of the Prospect Park revival of All My Children, it was revealed that Marissa had died and that she was the one who JR shot in the ABC series finale.