Because of this her echo gets through (6)
I believe the answer is:
hereby
'because of this' is the definition.
(I've seen this before)
'her echo gets through' is the wordplay.
'echo' becomes 'e' (phonetic alphabet: alpha, bravo, charlie etc.).
'gets' says to put letters next to each other.
'through' becomes 'by' ().
'her'+'e'+'by'='HEREBY'
(Other definitions for hereby that I've seen before include "By this means or act" , "Not far off" , "By means of this, legally speaking" , "By this means, as result of this" , "(Formally) with this" .)