could there be depression in infancy that is preventing her from being happy?
question is what is causing it? the parents give her everything she needs, emotionally, physically, etc…
In that case, there is little reason for her to have been depressed (withdrawn) as a baby. Is it just that she never smiles, or is she never happy?
Either way, presumably her parents have discussed this with their doctor and possibly other professionals, so there is no need for their friend – their very well meaning friend – to worry about it.