Prasad is after all prasad, even it is given to anyone by the enemy one takes it, so I don't think Madhu was wrong.One of my friend from different religion throw Prasad, when a Hindu gave her and that was not considered as a right thing, though no one said anything to her, but nobody in the group liked it.
It is individual decision to take prasad or not , Radha is well aware of customs and they are not in cordial terms to practice niceties . People refuse prasad in many instances specially girls do it during their periods or if you have not taken bath, if you have already eaten non veg etc , personally I did not like mAdhu forcing her mil . I don't have a problem with MAdhu taking prasad.
I don't want to comment on your friend by I do ask people if they are from different religion , if they want to take of not . I have seen many do not take .