Both her and Stoyanova are from Levski. It's the 2nd powerhouse in Superliga women's division. Both girls are also represented by Top Volley.
Kaya Nikolova and Boryana Angelova are currently much better than Mitkova but Plovdiv's president Dinkov is a greedy idiot. He blocked Top Volley's negotiations to transfer Plovdiv's best players to Italian league since they are the champions and he doesn't want to lose sponsors and money to Levski.
Angelova is American I don't know why she's in Bulgaria at the moment but she's definitely American. I can't remember what agency she's with I've seen it before... it's a US partner of a big agency but I can't recall which corny name it had. She probably wants to play in the US. Her sister is also in the US.