Bisexual is the most likely. Otherwise could be supporting someone or they meant this emoji instead 🌈

Support for the community and/or people she knows in the community.

Because she's showing support for others.

Showing support for the LGBTQ+ cummunity. Being straight AKA cis-gendered doesn't in any way put one in opposition to the non-cis- community. In fact I think it's a little weird to presume that the cis- wouldn't support the non-cis-.

In support of a friend or family member?

She probably wants people to know she is bisexual. Marrying a man doesn't make someone stop being bisexual. Bisexual people are constantly being erased. She is no less a part of the LGBTQ+ community for marrying a man.

Most likely bi or pan

It can mean a hundred things. And it goes up every week.

You can be an ally even if you aren't a part of the community.

Solidarity possibly for a friend who is LGBTQ++

not all rainbows mean gay

She likes rainbow cake.