I may be wrong and I'm sure I will be corrected if so, but unless your mother is looking to mortgage the property etc I don't think its an absolute requirement to have the title deeds transferred into her sole name. As they were already joint owners, the property should automatically pass to her.
It depends whether the property is held as joint tenants or tenants in common. If held as joint tenants the property automatically passes to your mother and the title can be updated simply if needed. If the property was held as tenants in common then a Grant of Probate would need to be taken out for your father's estate to transfer his share in the property.
it is more usual for married couples to hold as joint tenants though.
I hold the view that better to deal with issues as they arise rather than wait for issues to become bigger issues.
If the title to the property is not registered in the Land Registry and was held as tenants in common, I suggest your mother deals with a local neighbourhood solicitor, recommended by someone to her, to have a look at the deeds and advise.