Constraints limiting mother's stays (7)
I believe the answer is:
remains
'stays' is the definition.
('remain' can be a synonym of 'stay')
'constraints limiting mother's' is the wordplay.
'constraints' becomes 'reins' (I can't justify this - if you can you should give a lot more credence to this answer).
'limiting' is an insertion indicator.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'reins' enclosing 'ma' is 'REMAINS'.
Can you help me to learn more?
(Other definitions for remains that I've seen before include "surviving old parts" , "Leftovers" , "Residue" , "Corpse; relics" , "Body after death" .)