Getting close to the crown prince is a time sensitive thing. From what I remember Veronica being away from high society for so long would hurt her chances at getting close to him and being able to give birth to the prince's child. For instance, if Veronica is gone from high society for so long they can't keep making excuses - if she's sick, then she's obviously not physically well enough to bear children. People could start rumours she could have gotten pregnant and hidden the pregnancy/had the child, making her not a virgin anymore. She could be mentally unwell to join high society. The longer she stays out of the spotlight the higher the chance the crown prince marries someone else, ruining their plans