After vehemently refusing several proposals of marriage, Joan joined the
Dominican Convent of Jesus in
Aveiro in 1475.
[1] Her brother had, by then, been given an heir, so the family line was no longer in danger of extinction. Still, she was compelled several times to leave the convent and return to the court. She turned down an offer of marriage from
Charles VIII of France, 18 years her junior. In 1485, she received another offer, from the recently widowed
Richard III of England, who was only 8 months younger. This was to be part of a double marital alliance, with his niece
Elizabeth of York marrying her cousin, the future
Manuel I. However, his death in battle, of which Joan allegedly had a prophetic dream, halted these plans.