I have a mini hen that has layed softshell eggs since the very first egg she ever layed. That's been over a year now. What's up with that. I'm new at this but I love it...
How long has she been laying? It's not unusual at all for new layers to produce thin-shelled eggs for a while.
What kind of feed do you give them? Laying females (and no other poultry) require supplements of calcium, usually provided in "layer feed," or given on the side in the form of crushed oyster shell. You can also dry and crush their own egg shells and offer those separately.
If you have non-laying birds in the group (young, male, old, molting, sick/traumatized & not laying), you should use "all flock," not "layer," because the extra calcium in "layer" feed will harm non-laying birds. Giving oyster shells separately provides the layers with calcium without harming the others.
Thin shelled eggs could be a genetic defect, a short-lived problem at the beginning of lay or recommencement of lay, a momentary flaw concerning one or two eggs now and again, or a calcium deficiency.