When Clio turned five, she was poisoned by her Uncle Ferdand on behalf of his son Malvek, ruler of Dolmara. The First Doctor put Clio into stasis, and she was woken every year on her birthday. Every time Clio woke, Allise helped her dress for her party. Clio didn't understand why Allise seemed to age so quickly.
One day when Clio awoke, Allise was no longer there. No one explained to her why Allise was gone. (PROSE: The Glass Princess)