When her father is killed by a brutal warlord, a sheltered princess must take over as queen of her kingdom and lead her knights against an army of violent barbarians to defend her kingdom.

At first glance, the plot would seem to be:

When a brutal warlord kills her father, a sheltered princess must take over as queen and defend her kingdom against a barbarian invasion.
(23 words)

As if the death of her father and the invasion are 2 separate crises by 2 separate parties.

But if the same warlord is also the invader — his goal is to claim country and throne for himself — then perhaps:

When a brutal warlord kills her father and invades the kingdom, a sheltered princess must fight for her throne and the freedom of her people.
(25 words)

A virtue of the 2nd version is that she is fighting for something greater than just herself; she’s fighting for her people, for freedom– more important stakeholders and stakes than her claim to the throne.? [That’s not an insignificant nuance in the way historical (and fantasy) stories are framed these days, btw.]

Whatever, the ambiguity as to the role of warlord in the entirety of the plot needs to be clarified.

Also, I believe it always more effective to cast a character’s action — even the antagonist — in active, transitive words.? So “a brutal warlord kills the father” rather than “the father is killed by a brutal warlord”.? ?It also saves 2 words. achieving? economy as well as effectiveness.

fwiw