*She looks healthy to me.
Of course she doesn't look 'normal' but that's because overweight people who are somehow offended by people with a healthy BMI and write letters about it are becoming the norm.
Why do we need a race to the bottom with short, chubby, unattractive models? Clothes look best on the opposite of this and they are selling a clothes.*
Yes, they are selling clothes.
That is the one and only purpose of Boden, to make a profit by selling clothes. Clothes that go up to a size 22. They are not there to form an opinion on what a healthy weight is or to give dieting advice to customers. They are there to provide what the customer wants, no matter what the customer's shape or size.
I strongly disagree that things always look better on thinner women, it varies in my opinion, but regardless I think selling clothes to most of Boden's target market would go better if they showed a variety of shapes and sizes. A minority of customers will resemble the models in either height or weight or general shape.
I used to think that nevertheless companies possibly needed to use thin models to create an aspirational image, but now with the greater range of models being used by some other brands, I have realised this is really not the case. I am much much more likely to buy something if I can see it modelled by people who are closer to my own size. My own size varies a lot but whatever it is I need clothes. As I imagine everyone does. So it makes sense to use a variety of different size models. Not because I am in any sense 'offended' by seeing people much thinner or fatter than myself, but just because it gives me more practical information for choosing which items to order. Especially important with mail order stuff.
I don't have a problem with the model OP found too thin, more with the general policy of identikit models being used. It is the opposite of 'body shaming' anyone to suggest that there should be variety. Boden need customer feedback on that, and I would guess they want it, although they may be too pretentious to ever really change.