As Hymie states, there's no need for the actual document to he handwritten. All that is required is the signature of the person making the will and of two witnesses who were present together when the will was signed. If your mother can't manage to sign herself, this quote is relevant:
"If you are physically unable to sign or make your mark, e.g. because of paralysis or because you are blind, you can ask someone to sign the will for you as your will but they must do so in your presence and in the presence of the required witnesses"
Source:
http://www.howtobooks.co.uk/family/wills/how-t o-write.asp
(Remember that none of the signatories should be beneficiaries under the will. A beneficiary will lose their entitlement to inherit if they sign the will, either on behalf of the testator or as a witness).
Chris