Is it normal to feel insecure when dealing with unreliable friends?

I have a friend and we both have sons the same age and I like when they play together. But lately every time I ask her out or for a get together, she turns it down and says that she will come over during the week after work . . .So I wait and wait and the week goes by and she doesn't come over. She is planning to get married in April so I know she is busy with planning etc. but this happens every time lately. She doesn't even call to say she is not coming over when I expect her to come over. When I try to call her cell phone, I never can get through. It feels like a struggle to meet up and yet I know I am invited to the wedding. I don't know. Part of me feels like I should wait after she is married and the stress has passed but a part of me feels like I should tell her that if she can't make it over, she should at least call. And apart of me feels like it is somehow me and she doesn't want to be my friend and this is her way of telling me that. For my son's birthday, she and her son came over to the party but she didn't even bring him a gift. She apologized and said she was busy and didn't have time to go shopping, which she was I am sure but even after that, she could have come back with one on another occasion but instead she doesn't and she makes plans but doesn't follow through. Does she even want me at the wedding? Maybe she is trying to get me to cancel on her and not come.