The 33 days consecration is a very good devotion to Mary. One can do that anywhere. There is no requirement to go to Church or anywhere else to be consecrated, especially for your mother who has mobility difficulties. Of course, it would be nice to do it with others and to have a priest receiving the consecration, but one can equally be blessed praying the prayers at home and making the consecration alone.
As to having sins forgiven, that is a different thing altogether. What she needs is to either visit a priest or have a priest come to her home and to receive the sacrament of reconciliation. The consecration prayer does not forgive sins.