Hi, London! So sorry about your worsening arthritis! Are you receiving treatment for it?
Regardless, I can imagine how difficult that triple trainride must be. On the other hand, I know it can be difficult for a young mum to travel w/ a child. Besides, no matter what your partner thinks DD (dear daughter) should do, most likely, she's going to do what SHE thinks she should/needs to do. You could ASK her to visit more often, but chances are, she'll decline.
So, IMO, any change will have to be on your side. I suggest cutting back on your visits (w/o insisting that she increase hers). Right now you go to her 4 times a year or more. Perhaps cut back to twice a year and stick to that for a while? See how you feel? It will mean you only see DD and GD in person 4 times a year (their 1 visit and your 3), but it might make things easier for you. Maybe let DD know you're going to try cutting back b/c of your arthritis, but it's not written in stone. If the 3 visits are still too much, you might cut back to twice a year, etc. Or you might add that 4th visit back if you miss them too much and DD is ok w/ it.... Food for thought...