According to her Diary Book, she just met her father for some days.
Previously she was living alone on the woods, until she found two werewolves that agreed to help her. She lived with them and learned their customs, they said that the vampires were starting to hunt down OTHER mountrous creatures like werewolves, because humans were becoming rare. The werewolves were going to do a meeting to see what to do.
These 2 werewolves learned her origin and made the Nightsphere ritual to summon Abadeer, s he could be reunited with Marcy.....and the first thing that he did....was fucking eat their souls.
Marcy was horrorized, but her dad made execuses for it. The next days he explained her origins, talked about her mother, and Marceline started to feel conflicted, for one side her father was super charming and really loved her, on the other, he fucking killed her friends. She decided to accept him as just a "force of nature".
She them decided to try to use him as a way to help werewolves. They went to the meeting in the middle of ruins, and Abadeer said that he would end their problem with "vampires".
What he did? He ate the fucking souls of everybody.
Marcy was horrorized, but her father just said "now they dont have to care for vampires." Marcy was overwhelmed, and went to some ruins where she found fries, she left for some time and her father ate them.
She was tired of this bulshit, and just banished him for good, until Finn summoned him.