I think the salient part, that negates the "but it's the daughter's wedding, not the friend's" issue is
I thought we were the best of friends. She has other close friends, and I know them too. They were all at the wedding.
She has cause to feel left out by the friend, not the daughter, if all the close friends were invited. I think it would be less confrontational and thus a little easier to let her friend know she's sad she didn't get to be there. The friend in turn can choose to give her a reason why she wasn't included with the other friends, respond with something else to let her know she is a valued friend, or ignore it. It's hard to learn someone doesn't value you as a friend as you value her, but LW needs to know if she is to protect herself from being hurt by this friend again.
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I thought we were the best of friends. She has other close friends, and I know them too. They were all at the wedding.
She has cause to feel left out by the friend, not the daughter, if all the close friends were invited. I think it would be less confrontational and thus a little easier to let her friend know she's sad she didn't get to be there. The friend in turn can choose to give her a reason why she wasn't included with the other friends, respond with something else to let her know she is a valued friend, or ignore it. It's hard to learn someone doesn't value you as a friend as you value her, but LW needs to know if she is to protect herself from being hurt by this friend again.