How do you deal with being the single sister caring for you mother full-time while your other sisters is living her happily married life?
Jacqueline, I couldn't believe that, in addition to your other suggestions, you didn't suggest that the married sister should either travel the 1000 miles and buy her single sister a well-deserved holiday or else PAY for someone to care for the mother while the single sister went on a holiday paid for by the married sister. Surely at some time in the six years, the married sister had taken holidays. Did she ever think of taking her single sister's place during some of those holidays??
And how patronizing to suggest that the married sister ask her single sister for advice "even if you don't really need it".
My advice to the happily married sister running a successful business would be to get off her butt and give her single sister some relief!!! If she truly can't be there and since she runs such a successful business, then she can afford to hire someone to relieve her single sister. Do something practical about feeling "so guilty".