Also vitamin c won't do much when the grandma is already this weak and almost gone for good. An orange won't revive her from the dead.
If your body gets this weak and you're a poor beggar in a medieval world you're done
Some people seem to be wondering why she knows about scurvy but that fact is fairly well known, it's not exactly strange for someone who isn't a doctor to know how to cure it... Probably just learnt about it during history class or something.