Blind people probably would know the difference if they scrutinised the change they got but then the vast majority of people don't, it's easily possible for them to be given a £5 note back instead of a £10 and just stuff it in their pocket. But I'm not sure how this thread has got onto this topic anyway, it's completely irrelevant
Anyway there's no problem with what Jay's Mum is doing, it's natural for family members to try and get support for their relation