Unlike most, though, she has a large blue "CR7" tattoo just below her left collarbone.
And when the 20-year-old has children, she says she plans to call them Cristiano and Ronaldo.
Cesar was in the crowd late on Friday when the Portuguese team arrived at their hotel in Manaus ahead of Sunday's World Cup Group G game against the United States.
Cesar, who held a home made "There is only one Ronaldo" poster, said her fascination with the photogenic 29-year-old forward started when Portugal beat England on penalties in the 2006 World Cup.
"He scored a goal and dedicated it to his father who had just died. Well, from that point on, I got interested in his story, I started to get interested in order to understand," she told Reuters Television.
To help show her dedication, she got the tattoo in April. The seven in CR7 refers to Ronaldo's squad number with Portugal and Real Madrid.
"It did hurt a bit but all pain is bearable for him. And I loved it, my new tattoo," said Cesar.
(via @YasmimCesar on Twitter)
Perhaps not surprisingly, Cesar's mother Ednilda was not at all impressed by the idea.
She eventually agreed, however, on the grounds that Yasmine might otherwise "do something crazy or foolish".
The tattoo features prominently on Cesar's Facebook page. Her bedroom wall is covered with photos of the player and she has dozens more stored away.
"There are people in Brazil who say Cristiano Ronaldo is arrogant ... but for those who really know him he is a nice guy," said Cesar, who is studying to become a sports teacher.
Cesar bought a gold coloured necklace with a cross to give to Ronaldo but did not manage to get anywhere near him. Just seeing the player was some consolation, though.
"It's like a dream come true, it has been 10 years, so I still can't believe it," she exclaimed.
Portugal, who were thumped 4-0 by Germany in the first game, needs at least a point from Sunday's game to stand any chance of qualifying.
"I still think Portugal will make the quarter-finals. I would really like him to score a goal," said Cesar.
- Sports & Recreation
- Cristiano Ronaldo