Matriarch possibly needs thousand marks extra (11)
I believe the answer is:
grandmother
'matriarch possibly' is the definition.
(a grandmother might be the matriarch of a family)
'thousand marks extra' is the wordplay.
'thousand' becomes 'grand' (synonyms).
'marks' becomes 'M' (former German currency).
'extra' becomes 'other'.
'grand'+'m'+'other'='GRANDMOTHER'
'needs' acts as a link.
(Other definitions for grandmother that I've seen before include "Mum's mum" , "Older relative" , "Female ancestor" , "Proverbially competent egg sucker" , "See 22" .)