A young girl has the ability to create reality through her sketches, now her mother must protect her child from secretive agencies that want to exploit her power.

I agree with the question of who is the protagonist. Answering that will help you focus the logline. When you say that the young girl has the ability to create reality from her sketches, you are being too vague. Young to me can be anywhere from 4 to 15 or so. And there's quite a bit of difference between those ages. Ability to create reality makes me think she can create whole new worlds. Maybe you mean more like alter reality, or bring things from her sketches into reality. I just don't know. Also, as has been pointed out to me during my attempts at a logline, it is a good thing to show the protagonist as having some kind of character flaw. An autistic girl. An overprotective mother. It's pretty wide open, but anything here will add to the character and make them more interesting. I just don't like the use of the word secretive in this example. It strikes me as awkward. A secret government agency. A secret cabal.
Hope this helps.

Good start and good comments. As it is the mother appears to be the MC. Also, not sure how to interpret "protect". It could be physical, (the agency is trying to kidnap her), or it could be financial (bribe the daughter), it could be intimidation ("we can make your life hell"). It is probably all three.

Also can't the daughter just create a drawing with Agency out of the picture? Seems like she has the power to take care of herself --unless she is immature and having a tiff with mom.

An interesting idea. The phrase "secretive agencies" seems like it could be worded in a more interesting way. Maybe a more specific agency or someone specific from one of those agencies?