What does nu har det brunnit rejält mean?

See a translation

Now it has burned a lot!

@ellike1234

Oh yeah, you're right.
Sorry, I was just tired when I wrote that and thought they meant it literally.
Excuse me!!!

Well, often when you say:
De brinner för något

it means: They are really engaged in something interesting that they like

or

Det brinner I benen på dem

they mean that the person can't sit still, they have a lot of energy.
(At least that's my teacher always tells us.
our class is chaos. XD)

so I guess the idiom you were asking about could either means:

She's been thinking too much about it and she's worn out or about to burn out.

or:

that she has a lot of ideas, energy, is very engaged in something.

kind of like when you say there's fire in someone's eyes except in the brain.

it really depends on the situation

sorry that was long