Maroon Clown with a swollen butt

[chava67]

I noticed my female clown has a swollen butt with a reddness. What can be causing it?
I removed her from the tank to start treatment and reduce any additional stress.
Any recommendations?

 

[gweston]

I she an egg layer? My female Occelaris gets an enlarged gut and gets what appears to be a slightly prolapsed derriere when she is about to lay eggs.

 

[chava67]

Yes she has laid eggs many time before, but I have never seen her belly swell like this.
I've had her for 12 years and has been paired for 10 of those 12