Emma Raducanu is currently ranked as the 83rd player in the world but she's the number one seed ahead of Elena Rybakina for example.
The British player was highly ranked before the US Open but a poor performance there caused her to drop over 2000 points and fall to number 83. It was a drop of 72 spots but she was still the number one seed for the WTA 250 event in Portoroz.
The reason why is mostly luck. She received a wild card for the event and at the time she was ranked number 11 in the world. As she's a wild card, that's the ranking that's been used for the draw putting her ahead of Beatriz Haddad Maia and Elena Rybakina.
If the draw had come out after the ranking update happened, Raducanu would have been the 5th lowest ranked player in the main draw. It remains to be seen whether Raducanu can use that bit of luck to her advantage. She started off well, advancing past Yastremska in round one.