Being that Klaus was involved the whole time,Klaus compelled him to act that way and now she was happy after the task was done and she got the chance to say goodbye to Alaric and Elena. She got the chance also to say that she loved them all along, She did work for klaus and did her job but she also wanted to help Elena deep down because she loved her. I could be wrong but I think she chose to kill herself and die.
She meant that she was free , because she wanted to die and wanted to be relased from the world as she once had humanity and love and she abonded it and she left her daughter who she regreted..she had nothing to live for and once she کہا she was done she was reliffed
She was compelled سے طرف کی Klaus's servants to lure Katherine and the moonstone to them, then kill herself. After she did it the guy called her and کہا she was done. She کہا one last word to elena and killed herself.
Maybe she wanted to die because she didnt want to risk Klaus compelling her to hurt Elena again. She'd کہا her goodbyes to the ones she loved- told Elena that it was hard for her to give her up, and told Alaric that she had loved him. She finally realized that she'd lost all that she once was and decided not to live without it.
Klaus compelled her to fool all of them to get Alaric. Then, when the warlock called her and told her that she's done, he meant that what Klaus compelled her to do is already done, so she's free of her duty now. And what I think is that she actually loved Elena and Alaric and hated herself for doing this and planned to kill herself after Klaus compelled her. So when she کہا "I'm done" that means she is happy to finally pay herself back for all the bad things she did سے طرف کی killing herself. Hope I helped :)
She was tried of having herself torn between Klaus..who would kill her if she didn't do what he told her to and between her own flesh and blood-her daughter, Elena. SO she killed herself because she is so unhappy with herself and what she has done.