I’ve heard of this, it’s known as “late onset eggeritis”.
Basically she wasn’t actually laying for the last couple of years, but didn’t want to be known as a free loader, so she was sneaking off to town and buying store bought eggs and then slipping them in when no one was looking.
Now that little miss late bloomer is finally catching up, her tinted eggs have given her away.
She’s probably embarrassed about the past, but happy that she’s finally one of the big girls, so maybe just pretend you didn’t notice, just to spare her feelings, but have a talk with the whole group about the dangers of hitchhiking to town, and shoplifting from the grocery store.