Signal for the Swiss to turn on her plan (9)
I believe the answer is:
alpenhorn
'signal for the swiss' is the definition.
I can't tell whether this defines the answer.
'turn on her plan' is the wordplay.
'turn' is an anagram indicator.
'on'+'her'+'plan'='onherplan'
'onherplan' with letters rearranged gives 'ALPENHORN'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for alpenhorn that I've seen before include "Swiss wind instrument" , "Instrument for communication" , "What plays (over the heads of many)" , "It's a blast" , "blown up" .)