OMG. That was a lot of information to take it. Your 'friend' sounds extremely selfish. It sounds like she thinks she's doing you a favor by coming to your wedding now because she's in the area anyway. She should have been completely supportive of you in your time of loss and instead she was focusing on HER birthday party. Ridiculous.
That all aside though, it's YOUR wedding so the big question is despite all of this do you want her there? If you still do, sure, she can come. If you don't want her there, tell her politely that you have already booked all of your guests or something to that nature. If you don't want her friends there tell her it's invite only and if she wants to come she's more than welcome but unfortunately it would just be her, not her friends (it sounds like she's making this a party... it's YOUR WEDDING, c'mon!).
Me, personally, I wouldn't want her there... by the sounds of it she may end up causing more drama in the end.
That's just me though, you have to ask yourself if you want her there or not and act accordingly.
<3 good luck.