There's a mother! (7)

I believe the answer is:

theresa

'mother' is the definition.
(Mother Theresa, Catholic saint)

'there's a' is the wordplay.
'theres'+'a'='THERESA'

(Other definitions for theresa that I've seen before include "Maria --, Austrian ruler" , "Maria -, Habsburg empress" , "Woman" , "-- May, MP" , "Lisieux saint" .)

I've seen this clue in The Guardian.

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