Following the outbreak of a virus that wipes out the majority of the human population, a teen documents her family’s new life in quarantine and tries to protect her infected sister.

"Following the outbreak of a virus that wipes out the majority of the human population, a teen documents her family's new life in quarantine and tries to protect her infected sister."

This is a chronicle. Perhaps the chronicle of a death foretold.

We can make great movies with chronicles; espacially about survival; e.g. :
"The Pianist" by Roman Polanski,
"Grave of the Fireflies" by Isao Takahata,
"The Diary of Anne Frank" ( http://en.wikipedia.org/wiki/List_of_films_about_Anne_Frank ),
...

A particularity of most of chronicles is that it's not about transformation.

PROS
- Strong visual event.
- Impending confrontation with close relationship.

CONS
- Doesn't clearly specify use of found footage element.
- Lack of specific goal other than to survive.

The writer demonstrates an innate ability to deliver the story from their perspective but leads to a watered down logline that may cause issues with producers who are looking to check every element beforehand.

Your protagonist's goal is a bit muddied by "documenting her family's new life". Keep it primal, focused. The goal surely is to protect her sister? What is the end-goal of protecting her sister - as in, does that mean she's going to try and find a cure for the virus, or is there another threat attacking her sister while someone else tries to cure her? Who is your protagonist protecting her sister from?