I have cut ties with my oldest 'friend' recently. We have known each other nearly sixty years, she was bridesmaid at my first wedding in 1972. I don't believe she has had a very happy marriage, and have always thought she got married to the first man interested enough to ask, because she was the last of our class who was still single in her mid-20s. I moved around a lot, she stayed in her home town. At first there was lots of letters to and fro, then she got a job and the correspondence slowed down, but she always sent birthday cards and I never forgot hers either. Her career took off, from typist to head of a large department within five years, two sons came along also. All I ever heard from her was a card at Christmas with a one line message - always 'Hope you are well'. I accept she had a busier life than I, but once technology kicked in, she could have emailed regularly, just a quick chatty email every now and then. But no. Then she retired a few years ago, and I was so pleased as I thought it meant she might keep in touch now But no. So I sent a letter saying I wouldn't be in touch again as it seemed a very one-sided 'friendship' to me, and that wasn't the sort I wanted. Thought that might evoke a response, but no.
The point of this rambling is to say that it's perfectly all right to put an end to the friendship. We grow older and our priorities, what we expect from life, change. Friendships should make us happy, glad to be with the other person, to see them. If it's not making you feel like that, it's not worth it. You could write to her and tell her you won't be keeping in touch, and telling her why, as you put it on here. I'd give anything for a good friend I felt really close to, but sadly she died.