Welcome to BYC!
How many birds do you have?
If all the rest are laying fine, it's not their diet, so no need to change feed.
But knowing what
all and how exactly you are feeding can help here.
Some birds just have issues, I have had a few birds that laid wonky eggs full time.
Something is not up to snuff in the way the uptake/process the nutrition they are getting. It can be impossible to tell what the issue is, and often nothing to 'cure' it.
Could be caused by a genetic malformation or
maybe disease.
When I have a bird that is not up to snuff I isolate bird in a wire cage within the coop for a day or two....so you can closely monitor her intake of food and water, crop function(checking at night and in morning before providing more feed), and her poops. Examine the body
closely for bugs(part feathers down to skin around vent especially), belly bloating, anything that is not 'normal'
I like to use a
fold-able wire dog crate (24"L x 18"W x 21"H) with smaller mesh(1x2) on bottom of crate under tray.
Then you can put tray
underneath crate to better observe droppings without it being stepped in.
If smaller mesh is carefully installed, tray can still be used inside crate.