Is this weird at a wedding?

Yes, weird.

There shouldn't be anything tying her to the family already unless she's personally close to the ex-husband's brother's family.

Woman attends the wedding of her former niece (by marriage). Her ex husband was an asshoIe to her, but is dead now. No, it's not odd she'd attend the wedding if she were close to any of her in-laws or extended family.

Not knowing her history with any of those people, it's hard to comment.

Every one has a preference and a choice --- but to leave an ex behind - and to start a new life with a new person - the person should consider and think of their new life (not the old life).

She might be found of the ex-bro-in-law daughter ... however, your feelings should come first. If you have a problem with it - she should put you 1st. If you absolutely had NO problem with it - then it would be ok for her to go.

The word EX has a meaning defining it.

Not really, the bride presumably grew up seeing this woman as her aunt. Whatever happened later on, I would presume this woman was once an important part of the girls family. My fiance's uncle is invited to our wedding, even though he is long divorced from his mums sister.

Its not weird

she would be the brides aunt, why wouldnt she go?

the bride and aunt are obviously mature enough to have remained friendly

If this person i still friends with this brother and family, then it's not weird.