My pup was spayed two weeks ago at the age of six months. She has developed
a lump about the size of a golf ball under the line of the scar. It can me moved around internally.
Is this normal, has anyone else experienced this ?

See your vet, it may be an incisional hernia or an abcess, only an examination will tell.

I have just phoned the vet, and they reckon it's quite normal. a reaction to the internal stitches etc.
So long as she's ok in herself then i'm not to worry......easier said that done eh!?