After a young heiress unleashes primal powers, she is visited by a mysterious stranger and learns she must take on interdimensional beings that want her dead.

It’s unclear if the heiress unleashes “primal powers” in herself or in the world. I’ll assume the latter — in which case it’s also unclear if the unleashing is what opened the connection between our dimension and the other.

Your LL spine is:

“A young heiress unleashes primal powers and takes on interdimensional beings.”

So let’s build from there. The protag is colorless, so lets add a flaw. Also, let’s add back in the antag’s motivation:

“A spoiled heiress unleashes primal powers and now interdimensional beings want her dead.”

I left out Mysterious Stranger because all it does is add a secondary character to the LL, which we can do without.

The LL overall feels weak, with several elements ambiguous or confusioning, which hurts comprehension.

I think the revision delivers everything you wrote (sans Stranger) in a smaller, punchier package.

Good luck!
Pitchpatch, 10PTT.COM

Let’s slot your words into the revised logline and see what happens:

A spoiled [???] heiress discovers she can manipulate the energy flowing through all things. Now interdimensional beings want her dead.?

I left the “spoiled” placeholder, because you do need some intrigue about the protag’s inner struggle or circumstances.

The LL still feels somewhat truncated. Needs a bit more. A ticking clock, and obstacle, a hinted-at twist… something…

“… Now interdimensional beings want her dead but…”
“… want her dead and…”
“… want her dead before…”

As is, the revised LL tips too far toward passive for the protag. What’s she plan to do with those powers?

But as is, the LL establishes an unusual and intriguing conflict. I mean, wow, those are some massively expansive and powerful elements you’re playing with.