After learning her mermaid mother has only a week to live, a disfigured teenager must choose between a conniving snake and a vengeful clown, the only ones who know where to find her.

How about something like this?

Rescued from a life of bullying and abandonment, a young girl with a great destiny proves her worth while searching for her estranged mother on a fantastical island located at the end of a rainbow.

How about something like this?

Rescued from a life of bullying and abandonment, a young girl with a great destiny proves her worth while searching for her estranged mother on a fantastical island located at the end of a rainbow.

I think you are trying to say the lead character only has a week to find her mom who is dying and there are only two possible guides who can find the leads mother, both of whom which are flawed.

However if that is the case, then the inciting incident would not be the cancer but would be the discovery that her mom is missing.

What DPG said.

Also, I can't get a clear picture of the story. What does she actually do? Choosing is a relatively short period of screen time and an inner process at that, what actions does she take throughout most of the story to that matter act2?

Choose between them for what? ?As an adopting parent, I'm guessing. ?But I shouldn't have to guess.

And what's at stake? Sure he's disfigured, but does that make him disabled, unable to care and provide for himself? ?And he's also a teen approaching adulthood ?so why can't he just ?fend for himself? ?How near (old) or far (young) is he away from that? Fending for himself seems to be the best choice ?- why would he want/need to rely on the other two, deeply flawed surrogate parents?