I think you can have your boundaries and help her when you are available. If she really needs something, like to go get groceries, you could always say "I'm going again on Tuesday, so you are welcome to come with me then." You don't have to go out of your way.

On the glasses thing, just tell her. "Hey, I wanted to make you aware that sometimes when you clean your glasses and you use your shirt, you lift it up quite high and your chest becomes visible." Most likely she will be a little embarrassed, and you can just say "I know I would want someone to tell me if my zipper was down or my skirt was tucked up or something." She will likely appreciate it.

Just be calm and maintain your boundaries. If she feels lonely or sad, that's not on you. You can have compassion for her, but you don't need to feel it for her. You are not responsible for her. It's amazing that you want to be helpful to her. And you may gain some friendship in that.

I moved in next to an elderly neighbor many years ago. I helped her do many things and ended up going over to her condo almost every day for drinks and dinner, that she would cook (she was an amazing cook). She is a great friend and quite a character. So, yes, her loneliness may be making her a bit clingy, but you can keep boundaries and still be a good friend if that's what you want to be.