Sounds to me like she is having no adults in the wedding party other than her own children.
That seems appropriate for a 2nd wedding.
I'm sorry they hurt your feelings by not including you, but if you aren't even close enough to her (or your brother) to ask why you weren't chosen for a bridesmaid, that there may be your reason.
I'm sure when your friends start getting married, you will have opportunities to help them on their days.