andyj1967
If you are not your wife's Appointee then you will have limited opportunity to participate in the assessment. Moral support cannot be underestimated but you should ask the question of whether your wife may appear more capable in your presence than if you are not there.
Be aware, if you do cancel this first appointment then she must attend any second one, whether it is convenient for you or not, failing to do so will result in her file being returned to the DWP and could result in her claim being closed.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
