It was announced on Tuesday that the 35-year-old - who has not displayed symptoms - was in isolation and out of Portugal's UEFA Nations League clash with Sweden after contracting the virus.
On Wednesday, Aveiro posted a picture of her brother on her Instagram Stories alongside the caption: "If Cristiano Ronaldo is the one who has to wake the world up, I have to say that this Portuguese really is an envoy from God. Thank you!
"I believe that, today, thousands of people who have come to believe so much in this pandemic, in the tests and the measures taken will, like me, see it is the biggest fraud I've seen since I was born.
"A phrase that I read today and that I stood up to applaud: 'Enough fooling the entire world'. Someone, open your eyes, please."
She also posted a video of Ronaldo's positive test being discussed on Portuguese television.