hello @Bekkimaria - welcome to BYC
that's a soft-shelled egg; it's quite common and there are several different causes.
How long has your girl been laying?
Soft-shelled eggs happen. Sounds like she's had a lot of changes in the last three weeks. Maybe once she's used to her new home, routine and diet, she will lay more "normal" eggs. Kudos to you for adopting her and caring enough to ask questions on her behalf.