She was a colossal disaster (7)
I believe the answer is:
titanic
'was a colossal disaster' is the definition.
I can't judge whether this defines the answer.
'she' is the wordplay.
I cannot quite see how this works, but
'she' could be 'tani' and 'tani' is found in the answer.
The remaining letters 'tic' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for titanic that I've seen before include "Nineteen twelve iceberg victim" , "Iceberg-hitting ship" , "Doomed liner found in attic" , "Of enormous size, like the stricken liner" , "Act in it (anag.)" .)