I'm assuming you mean "the second letter is 'u'". if so, could it be Aunties?
A sister?
EDIT: Thinking on the subject some more, I suppose a mother is also a female relative with 6 letters.
Niece (a sibling's female child)
There is no word for a female relative that begins with a 't'. The words for a female relative that contain 6 letters are: Sister Mother Granny
There is no word for a female relative that begins with a 't'. The words for a female relative that contain 6 letters are: Sister Mother Granny
Etcher
waddle
Massif
commonnovice
innuit
The Monkey King One Missed Call
6 letters 6 letters
Claire, Cherie, Connie
The dahlia has 6 letters.
The number of combinations of 6 letters is 6! or 720.