Yes, it is possible for females to produce something that really resembles a sperm plug. This came from a girl of mine, and since she laid eggs I'm pretty sure she's still a girl. (although it did cause a bit of panic on my part )

If you popped you want to look for the hemipenes to confirm the sex.

Also I'm a firm believer in quarantining. Even animals that come from very trusted sources go through QT in my house. (~3 months for me, but I'd recommend at least a month!)