I always thought Sexed Up by Robbie Williams would be a good one.

Love Will Tear Us Apart 💔 Joy Division

Round Round - Sugababes

Bye Bye Bye - 'NSync (boys anthem though but still suitable)

these ones are perfect!
Life Goes On
https://www.youtube.com/watch?v=kmVbEDLGIr8

Suddenly
https://www.youtube.com/watch?v=TKCwfnJ1exg

read the lyrics

and to a lesser extent, 10'000 angels
https://www.youtube.com/watch?v=nbeBlkrYmg8

Irreplaceable by Beyonce. "To the left, to the left, everything you own in a box to the left"

I'm Free - The Who

Mary J Blige - Not Gon' Cry

https://www.youtube.com/watch?v=WiM3bGcXYxk

Shut up and let me go - The Ting Tings

Maybe
Disco 2000 - Pulp
Die You Bastard - Motorhead
Grounds for Divorce - Elbow possibly
Hole in the Head - Sugababes
The One I Love - R.E.M (Not a love song!)
Fighter - Christina Aguileria

Better Days - Bruce Springsteen

Comeback - Ella Eyre

https://www.youtube.com/watch?v=KnnvfHz7qzA

Whatever by oasis.

Don't look back in anger by oasis.

Things can only get better by dReam

Substitute by the who. "substitute you for my mum, atleast I'll get my washing done"-great line.

You're History- Shakespears sister

This isn't really a divorce song but try 'Unhooked Generation' by Freda Payne. Great song.
'I just kicked the habit of being a fool for you.'

Also, Tainted Love (preferably the Gloria Jones version)

Memphis Tennessee - Chuck Berry

(in this song the singer is trying to contact his six year old daughter in Memphis, and it is implied, rather than openly stated, that he is divorced from her mother).

The obvious one:-

D.I.V.O.R.C.E - Tammy Wynette
(although I much prefer the parody of this song by Billy Connolly).

DJ. Jurgen ft. Alice DeeJay - Better Off Alone
Beyonce - Single Ladies
Beautiful South - A Little Time
Ed Sheeran - You Need Me, I Don't Need You
Erasure - Love To Hate You

I Don't Want You Back by Eamon - this was no 1 when Mini Deb was born.

Haitian Divorce - Steely Dan
Mexican Divorce - The Drifters
Release Me - Engelbert Humperdinck
You Don’t Bring Me Flowers - Neil Diamond and Barbra Sterisand

None of the above are really party songs (and the last two are more about relationships going wrong and an implicit desire for divorce rather than an actual divorce) but I thought I'd mention them anyway.

The best!

I'm going to wash that man right out of hair

https://m.youtube.com/watch?v=Zzu8ZxBHMWk

It would help to know something of the circumstances. Is it an amicable divorce, is she glad or sad, kind of thing.