spots in egg shell? (picture)

I had just randomly candled a recent egg my rouen laid, she has no mate but was at the vet overnight last week and there was a drake so figured i'd check just in case. The texture of the outside of the shell was smooth as usual, but when i candled it i noticed what looked like spots in the inner shell. I recently have been giving her oyster shell every couple days since she's been having problems with egg bind the past month hoping that will help and have read too much calcium can cause a rough texture but it seems to be the inner shell. Just wondering if it is the calcium intake or something else. Thanks!