Yes, if you have a parasite infestation it can cause a bird to stop laying. If you think you have bugs, treat all your flock because what one has, so do the others.Will lice cause hen to stop laying completely? She's young. Just started laying this spring and layed almost everyday for 3 almost 4 weeks. Now nothing for 3 weeks. She's not molting. Though I did add 4 "dumb" hens to my mix lol.
Also, if there is a flock change, i.e. adding new members, that can stress a bird and cause them to quit for a while. Just check to be sure she is not being bullied by the new additions.
Hope that helps. Good luck.