Weirdo “thing” found in pullet necropsy... What is it?

It's a lash egg. Pus and dead cells. Probably an infection. Sorry to hear about your bird... Horrible.

 

Yes, looks like a lash egg, likely caused by salpingitis. I'm sorry for your loss.
Most of the time when birds become symptomatic the infection has become too much for successful treatment and it sometimes happens as with yours that it isn't discovered until necropsy. This seems to be more common in hatchery birds that are bred to be prolific layers.
http://www.poultrydvm.com/condition/salpingitis
http://www.the-chicken-chick.com/2015/03/causes-of-lash-eggs-salpingitis-by.html

 

Agreed - looks like Salpingitis to me. @coach723 has given you some very good links to read.

@chickenmomma16 I'm sorry to hear about your hen but I'm glad you were able to open her up to find out the cause. The photo and your information will be helpful to others.
(can't help but smile at your title though - "weirdo thing")

 

So sorry you lost your hen! I have no experience with lash eggs but I agree with everyone else that's what it looks like per the many pictures I've seen on here.

I just wanted to say good for you for being able to do a necropsy on her! I see many posts on here where a bird will die and the owner never figures out why it died. That would drive me crazy not knowing the why!

 

It would be interesting to cut it open. There are many pictures of lash eggs if you Google lash egg images. Cancer in the reproductive tract is another common cause of death in hens. Good for you doing a necropsy. I have done a couple, and they are not for the faint of heart, but can be very helpful in identifying a cause of death. Sorry for your loss.

 

Sorry for your loss