Old lady not bending for dog (7)
I believe the answer is:
mastiff
'for dog' is the definition.
(breed of dog)
'old lady not bending' is the wordplay.
'old lady' becomes 'ma' (both can mean mother).
'not bending' becomes 'stiff' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ma'+'stiff'='MASTIFF'
Can you help me to learn more?
(Other definitions for mastiff that I've seen before include "Large, powerful, short-haired dog" , "Big dog" , "Powerful breed of watchdog" , "Powerful, smooth-coated dog used for security work" , "Large short-haired dog breed" .)