This romantic, sci-fi action fantasy is set in a medieval world where war is common and survival is a daily struggle. The young heroine, Betha must persevere to overcome beasts, barbarians, ice Vikings, mythical creatures, elves and savages throughout the kingdom who all want her head.

Agreed with all the above.

I'll add that in most cases when you find yourself using many adjectives or genre descriptions in a logline, you know something is wrong.

I think you need to tell us 'why' all these creatures want her head. What is so special about her, or what is so special about her mission/goal that everyone wants her dead?

What are they trying to stop?

Take this as an example: "When she discovers she's the descendant of the last dragon, a headstrong village girl must..." then tell us what her goal is and what she must do to achieve it.

We don't need names in a logline. It takes up valuable words - a logline should ideally be under 40 words. If there's a certain amount of world building required to understand the story then, obviously, go for it. It's a guideline only.

Check out the formula page to help with how a logline should be formatted. The main things we need though are an inciting incident (something that kick starts the story and poses a question for the protagonist), a protagonist, and a goal (that is the protagonist's answer to the question posed in the inciting incident).

Currently, all we have is a situation where your protagonist is simply avoiding being killed and battling people/creatures. To what end? Why do they want her head? What's she trying to achieve? Who is Betha? How young is young? 8 or 20?

It's more Fantasy than SciFi. SciFi, to me, is taking the world as we know and advancing it in some or many scientific ways. Space travel, aliens, futuristic worlds, etc. etc. I think setting it in a medieval world with mythical creatures - this screams Fantasy. Game of Thrones is a Fantasy. Not a SciFi. It might seem trivial, but if a production company are looking to make a new "Game of Thrones" type show and they search their loglines by genre... yours won't come up.

Where's the romance element?

Ultimately, I think we have a good idea of the world but no sense of the story. Story is the most important thing in a logline. A logline IS the story - albeit condensed into 40 words or less (ideally).

Romantic sci fi action series set in the medieval times? That's a tough sell.