Ms Nightingale was first to ensue (4,2)

I believe the answer is:

flow on

I'm a little stuck... Click here to teach me more about this clue!

'ms' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's a link between them I don't understand?

'nightingale was first to ensue' is the wordplay.
'nightingale' becomes 'flo' (I've seen this before).
'was first' becomes 'w' (ost letter of 'was').
'to ensue' becomes 'on' (I can't justify this - if you can you should believe this answer much more).
'flo'+'w'+'on'='FLOW-ON'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app