She's often on the line (3)
I believe the answer is:
peg
'the line' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I don't see?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for peg that I've seen before include "Wooden or plastic pin for hanging clothes" , "Kind of pin for hanging clothes" , "Brandy and soda drink measure" , "Old song: ''... o' my heart''" , "The girl to hold a hat" .)