In reply to apana790: I guess it doesn't matter how durable the boots are if they don't fit right. Recommending a durable boot - the Delta's are a good choice (as might be the Keen's), but as she has found, they need to fit right. Whhat is it that she is finding uncomfortable? Tightness, blisters, tiredness, pressure points? It would be worth looking at that before looking for new boots.
I'd also recommend taking them into a Cotswold store and getting a proper boot fitting. They'll do it on her Delta's, to check the fit for her, and can maybe correct what is wrong with them.