She’s 61. I find it interesting that you are referring to her as “a girl”. Why?

It’s possible there is something wrong with her or something went down but in a long run why does it matter? You can’t make her date you. I’ve met men who were convinced that me saying “no” to dating them wasn’t really valid and they need to continue pursuing me despite me not being interested. Rejections are hard but fighting it isn’t going to resolve it

Of course she liked you but does it mean she must continue relationship with you? For whatever reason she just decided against it. Maybe she decided that starting relationship in her 60s just isn’t worth the hassle. Maybe her family influenced her. Maybe it’s something else. But there’s not much you can do about it

My best friend is a single 60 something woman. She decided she doesn’t want to date at all and will not get into relationships anymore. She lives a very busy exciting life. She doesn’t want to entangle herself with a man. There is nothing wrong with her. It’s a perfectly valid option to stay single as well as option of staying friends. Maybe your lady decided it’s too much work

Also many older people with comfortable life style don’t want to start relationships because it might mean they need to take on and financially support another human being or they need to substantially alter their life style. Many don’t want to do that.