A disability or illness that prevents someone from going to Mass is indeed a valid reason to miss Mass on a Sunday or holy day of obligation. Your wife need not worry that she is committing any sin.
If your wife likes, she may ask her pastor if an extraordinary minister of holy Communion could bring her Communion on those Sundays and holy days when you are unable to take her to Mass. It is not required that your wife do so, but she might like to know that many parishes have programs available to take Communion to those Catholics prevented by illness and/or disability from attending Mass.
