That does sort of sound like flehmening. When Sammy does it he opens his
mouth, holds it open just a little ways, and looks like he's panting. When
Harri does it she curls up her nose a little. So I guess different kitties
do it a little differently.

Does she do it often? If so, it might be worth a visit to the vet.

Sometimes my Xena will do this when she finds an interesting smell.
Cats have sensors in the roof of their mouths that help with smell, and
opening the mouth and breathing that way helps them to smell.  I don't
usually  hear much noise when she does this, but it looks funny. Jennie

If she's only doing it when she's sniffing something strange to her, I
wouldn't worry about it. But if she just seems to do it for no reason
at all, I think I'd ask the vet about it.
Mine don't make a sound when they do that. They just look slack-jawed
and a little dopey. Like for instance, they'll do it sniffing my shoes
or pants after I've been around other dogs or cats.

Sherry