In Tam's short story it says she has black hair like Umber and (in nightfall? maybe) it says Umber and Trix are almost always together. it also says in legacy she is the most devoted to the neverseen probably because she would've grew up with them.
she also trusted lady Gisila, i am assuming that is because she has known her for a while and Umber might of also trusted her.
she could've also manifested differntly
(marella was different from her dad and mom so it is possible)