Retry with problem on my friends apple tree what she do about this blight?

looks like wolly aphids, if a small area use a brush on solution of malathion or a larger area a spray on systemic insecticide.
according to my books.. maybe someone else can be more specific.

Have to be a bit careful what you use on fruit trees. Apples particularly prone to wooly aphid. I read somewhere once that planting nasturtium nearby can help because the aphids prefer them.

I'd spray with an insecticide that treats woolly aphids, but if you want to use the apples from that tree, don't buy anything that says its "systemic" - this will penetrate the sap stream of the tree and be present in all its tissues, including the apples.