As I understand it, Juana's mother Queen Isabella, didn't visit her own mother from the time she and her brother were taken by their brother, Henry IV, to the court in about 1461, until the time the old Queen died in 1496. 'Madness' or depressive illness was a frightening thing at the time and quite impossible to cure - it's hard enough today. It could be viewed as the results of a curse, as a punishment from God, or any number of unpleasant things. Isabella had to fight for her inheritance, pull together two kingdoms, and fight the Moors, and highlighting the relationship with her 'mad' mother was not the best way to show that God was on her side. Putting your children anywhere near your mad mother was also unlikely to be perceived as a caring maternal gesture in that day and age. I could be wrong, but everything I've read suggested that Isabella of Portugal was looked after, but kept very much under wraps; she wasn't visited routinely by her daughter, and indeed, didn't recognise her when the Queen finally attended her deathbed. Even if she had met Juana, it's very unlikely she would have been able to sustain any kind of relationship given her condition.
