If her pension then falls below the minimum income set for pensioners (which is higher than the basic pension rate) she can apply for pension credit that will bring her weekly income up to a minimum of £155.60 plus an entitlement to help in paying Council tax and her rent, if you rent your home.
While I trust, widowhood is long in the distance for your wife, the best thing she can do when that happens is contact her local Age UK (previously Age Concern) and get them to help and advise her. They would do a benefits/pension check and help her apply for any benefits she may be entitled to.