hi how much food do you recomend for a westie, we tend to give her one tin  a day?

Personally I would never feed tinned food as it is mainly water.  If you was to boil up a can you would be surprised at how little actual food you would be left with.  Do you feed biscuit meal with your tins?
Also I would find it hard to advise what to give because each brand varies but there should be a guide on the side of the can, then be guided by your dogs condition, health and vitality as to whether you feed more than that or less.
I would advise changing to a good quality complete meal, that way you will know your dog is getting all it needs and it will work out much cheaper too.

Bev