How can I get my only sister to call our mom and show interest in her more often?

I have to agree with the others in that you have no control over your sibling. Ultimately, she is the one who is gonna have to live with herself and she may never feel regret or guilt. I know my two sisters never have as I am in a very similar situation. My one sister even lives less than a half mile from my mother. But bottom line is you can't force someone to have compassion, love, a sense of duty, etc., etc. Good luck to you and know that you are so not alone with this type of issue.

Jan, Shedevil is right - you can't force your sister to do anything - even send checks on time. I am in the same boat with my brother, he lives in the same town as Mom and brags about how much he does for her yet I can count on one hand the number of hours he's seen her in the past 3 months. Neither her or his family even CALL her. I live across the country and have spent much more time with her! Needless to say, I don't care if my relationship with him lasts after my Mom passes away. I doubt he'll feel guilty either because he's just too self-centered to give a damn. You have to be content with the amount of time you spend with your mom; it's hard but consider that at least she has you, some others have no one at all.

i also read your profile and noted that all of you contribute to your mom's care. Perhaps that's a burden she can hardly bare. To ensure that all of your relationships last past Mom's death, you might consider state assistance for her assisted living costs. Paying her rent is not an obligation that the kids MUST take on. It's an honorable and loving thing but given today's economy. Best of luck to you all

My mother-in-law is also in an asst living facility. Due to her dementia which is causing her short term memory to go 'belly up' she can't remember who calls and who doesn't anyway. Usually she says that 'nobody calls me' but that's NOT true, she just can't remember. So as your mother's dementia progresses, it won't matter if your sister calls her or not. I read in your profile that you have to remind your sister to send the check. First of all, tell her how grateful you are for the money, and anything that she DOES for you and your mom, since you have no power over the things that she doesn't do, concentrate on the good things. As far as the money being late, just remind her that setting the option up online with her bank to automatically pay a certain amount to a certain place is a lot easier than trying to remember who gets what and when.
I usually pick my m-i-l up a few days a week and take her places for fun. She also spends Sunday's with us, starting with church and lasting sometimes all day. There is no need for me to be there everyday and babysit her. She is ultimately the one who chooses whether to sit in her room and watch TV all day, or get out and socialize. Good luck, I wish I had better idea for you, but getting old stinks and there's not much we can do about that. :)

Dear Jan,
Unfortunately, you can only controll your actions, not your sister's. Talk to her and give best try to convince her your mother needs her and wants to see her. If she refuses, that's as far as you can go. Please don't wasted precious emotional engery on something that's not going to change. It will be your sister who bears the guilt of her decision. Be strong and stay committed to yur mother and let your sister walk her own path. Good Luck. SM