My puppy was reunited with her mother dog after 3 months away as I needed the breeders signature on microchip forms. The mother dogs tail was wagging at first and she seemed happy to see her pup but as soon as pup was off leash mum started snapping and growling at her. Any ideas why? I had this picture in my head that mum would be so happy and they would have an amazing reunion but didn’t happen that way!

Sounds perfectly normal, your pup was probably a bit over enthusiastic in greeting and Mum is just teaching her manners. A pup I bred lived in the same village and we ran into them often, even at 13 years old 'pup' was still delighted to see her Mum, trying to lick Mums lips, teeth etc and Mum was always telling her off

Sounds perfectly normal to me.

Very sadly in the animal world, this rarely happens.   You might have hoped for an aaah happy reunion, but fact is once an offspring has gone off to a new life, it smells totally different - different surroundings, different food.    I'm assuming this puppy hasn't come back for good because your bitch has every right to treat any 'new' dog coming in the way she has.   I remember one puppy who came back with his owners to show us how he was developing (that didn't often happen!) and as he came across the doorstep, mum started talking to him and it sounded exactly like how any mum might talk to an offspring - 'where have you been, why didn't you phone or write'..........  truly.

I don't think your bitch was telling him off - in any way other than she might have done with another overly familiar 'intruder'.

Pup is also a little older now and losing the leeway that comes with puppyhood, so adults get less tolerant with them, regardless of family.  More boisterous means less tolerance!