Could anyone please advise. I have a six month old Westie Bitch, who has always had a good appetite (but not greedy) - and only recently has been put onto Natures menu which she seemed to really enjoy.

However, over the last week she has become very picky at meal times, and even left her food altogether.

I do not feel that she is in anyway poorly, as she readily eats anything we do.

I have tried changing the feed, but it isn't making any difference.

All her teeth appear to be through, so I don't think thats the problem.

I was wondering if she may be ready to come into season, and maybe her hormones are playing up.

Any advice would be greatly appreciated

If she is in season it might be related, but I doubt it. I have to wonder why you changed her diet if she was happy with the original? She shouldn't be getting 'what we have', rather her own balanced diet for DOGS. Why not go back to the original. Never change a diet unless you have to. Dogs are creatures of habit and will happily eat the same food every day, though the odd addition of say a few vegetables or gravy is OK now and then.
Don't be tempted into trying her with all sorts of things. Provided she is active and healthy, she'll eat what she should, when she's hungry, without any ill effects.