A misanthropic girl and her rebellious friend are constantly looking for thrills to lighten up their dull lives but when she learns her half-sister has supernatural powers, she realizes having a normal life isn’t so bad.

Hello,
is this for a feature lenght movie or a short?
In my opinion this could be a quite accurate synopsis for a short.
As a feature lenght movie, I share the opinions of the previous commenters.
In detail, I'm not confortable with a character who "realize" something: this is 'internal', a logline should focus on the 'external' to attract me.

Loglines are about action, the intentional struggle for an objective goal, not about lessons learned which come as an unintended consequence. ? As suggested by Nir Shelter, the ?"Training" option at the top of this ?web page has guidelines for the elements that should go into an industry standard logline.

This logline doesn't describe an inciting incident (event) or a goal, and as such doesn't describe a plot.

What will she do? Why? And to what end? These are the vital pieces of information missing from your logline.

I can't make any suggestions as the are not enough details to go off.

Best if you define an event that pushes her/motivates her to take action in order to achieve a goal.

Check out the training tab up top for more information.