The hottest property in British pop penned her own No1 smash Do It Like A Dude and has written hits for US stars Miley Cyrus, Alicia Keys and Chris Brown.
Her offering for Britney's Femme Fatale did not make the cut - but Jessie insists she is not in the huff about it.
She said: "I think it's a misunderstanding. Just because I'm Jessie J, jazz hands, it doesn't mean I get pumped up to the top-three choice.
"It means that I write a song and if it doesn't go on it, it doesn't go on it. She probably had every major songwriter in the world write a song for her."
Jessie can't even offer the song to anyone else - or have a go at it herself - because it's titled Being Britney.
The British star refuses to let the snub get to her and is adamant she appreciated the opportunity - even though it didn't work out.
And she admits it's tough writing tracks strong enough for the biggest pop artists on the planet.
She also feels her own career as a singer means she does not have as much time to write as she'd like.
Jessie said: "To even have the opportunity to write a song for her is still incredible.
"As a songwriter, I'm still taking baby steps. You have to write 10 songs to get one good one and, realistically, I don't have time to write 10. It was a good song, though."
The really bad news is that now Britney has turned down the track, it's pretty much dead in the water.
Normally if one artist does not like a song, the writer simply offers it to other similar singers or record labels looking to launch new stars.
In this case, that will prove more or less impossible - unless she can find another signer called Britney.
Jessie said: "I may try to pitch it to someone else but it was actually called Being Britney.
"So it's actually hard to pitch it. It was a really cool song but it is what it is - it happens for a reason.
"For me, one thing I love about Britney Spears is she is Britney Spears - no one can come and try and steal her path, her lane and that's what I love about her.
"That's what the song is about, 'I'm the s***.'"
Hmmm... wonder if Whitney Houston fancies a shot at it?
