Any ideas what this is?

I’m posting for my sister. She had a tubal ligation a couple years ago but has been considering getting it reversed. Well she got an ovarian cyst and has had a couple ultrasounds to keep an eye on it. Today she went in for a follow up and no more cyst but the ultrasound tech got kind of weird and started asking about her last period and when her next is due. The tech told her that the doctor would be in contact to discuss the result. She looked at the ribbon of ultrasound while getting dressed and saw this little bubble. Does any one have any ideas what it could be? She said her pregnancy test was negative.