I think the clue is in the inviting you to be her bridesmaid bit.
Having suffered a couple of years of online bullying by my ex and my own sister, the thing I've learnt that they both have in common and reminds of this person you talk about OP, is that she probably doesn't have any friends at all, and struggles to make friends (hence her making you an instant bezzie), along with the exaggerated stories and constant 'life is so amazing'.
Life isn't amazing for them, they're so invested in their own fantasies because it makes up for the utter emptiness or unhappiness they're actually wading through.
You say her husband has cheated on her - perhaps she knows this, and is desperately unhappy about it. It would only take a few choice and sensitive conversations for you to figure out if she knows. If she wanted to confide in you about it, perhaps that would be the start of a proper, genuine, and honest friendship between you both.
Meanwhile, she's going through something, whatever it is, it's making her like she is. And making you unhappy, so it's not a genuine friendship if neither of you can reach a level where you truly connect.
Disclaimer: I don't have a single adult friend, so I may be talking complete nonsense. I'd love a friend, but I keep attracting people like my ex and my sister, so I've given up 