How upsetting for your friend! Is she in the States?
If he's taking EBM then I'd say it's not because of any change in the milk.
Was she using bottles at all before this started? He may have decided he prefers them. Otherwise maybe it's something going on with him physically...?
Is baby intrested in feeding during the night? At that age they get more interested in what's going on and have less time for feeding during the day often.
Has she tried osteo/chiro? Maybe he's uncomfortable. Or any illness (ear infection or something)?
Taking time out together as HotI suggests is a good idea too - a bath together, cuddling in bed. or try a totally different position - i remember kneeling over DS to feed him a few times when he went through a refusal stage.