Hey, Callum! I noticed a couple of grammatical errors so let me correct those for you before I give you my thoughts.

Here is what I believe to be a more polished version of your logline. Feel free to use what you like and discard what you don’t.

“When a mother discovers their home without a Christmas tree during the holiday, she goes to desperate lengths to surprise her daughter and bring back the Christmas spirit.”

As for my review, (and keep in mind that I am an amateur writer like you so take this with a grain of salt) firstly, it doesn’t make sense for the daughter to come home and realize that the tree was missing, causing the mother to go to great lengths to try and surprise her daughter. To me, it makes more sense for that to be her mother (I’m envisioning that the child is like six or something). Her mother upon realizing that there is no tree for Christmas then goes to great lengths to surprise her daughter so that way she doesn’t wake up on Christmas morning without a tree or any presents under it.

That also brings me to my second point which is that to me, it makes more sense that she realizes that she is without a tree prior to Christmas morning, and then has until Christmas morning to surprise her daughter. That way it gives some stakes and a deadline for your character so that way it conveys a sense of urgency for the audience.

Thirdly, as of right now, it seems like the genre that you have your film in (and I could be wrong because keep in mind that I haven’t actually read your script) is miscast. As of right now, it reads more like a Kids and Family movie or a Holiday Drama as opposed to a Holiday Adventure movie.

If you want it to be more of a Holiday Adventure movie, try adding a journey element into the logline to give us a sense of the adventure that she’s about to embark on.

For example, “When a mother discovers their home is without a Christmas tree during the holiday, she embarks on [insert some sort of thrilling quest here, like going through the city to get a tree, to the North Pole, etc.], facing [insert obstacles here, as a consequence of said journey], before her daughter wakes on Christmas morning.”

I hope that helps! 🙂

Respectfully, this isn’t a logline. A logline captures the essence of your story in a nutshell in one sentence, not to exceed 25 to 30 words. It gives a brief description of your protagonist, the goal of the protagonist, a brief description of the antagonist, and then the conflict/stakes.

Try this:

A psychiatric researcher voluntarily admits herself into an institution to investigate breach-of-care allegations, only to become the subject of a sinister experiment at the hands of twisted doctors.

As far as the premise is concerned, it sounds incredibly intriguing!