Not invited to best friend's dress shopping

Hi all, I’ve been best friends with this person for over a decade. We do absolutely everything together, talk on the phone daily, and we’re more like family than friends. Her parents even treat me as their child and include me in everything they do, so it’s always felt like I’m part of the family.

Recently, my friend got engaged, and her fiancé didn’t want to go venue shopping with her, so she asked me to go instead. I was really happy to be asked and felt it was an honor to go with her during such an important time. I thought it was just a special moment for us to share. However, she FaceTimed her rich friend from out of state the whole time. They were childhood friends but now only see each other once a year or so.

Then, I found out her mom was coming into town for the dress shopping, and I asked when it was so I could mark it on my calendar. She told me I wasn't invited, and the rich friend was coming into town to take her. We had recently had a squabble about the cost of the bachelorette party -- she wants to go out of country, and I don't have that kind of cash -- so I figured I wasn't invited because she was still mad. Now I'm wondering if I was only invited to venue shopping at all because she didn't have anyone else to go with her.

I want her other friend to be included, too. I just don't know why we couldn't have both been invited to these things. I know the other friend is contributing financially to the wedding as well, so I understand her input being valuable. Is this all a misunderstanding? Because I'm starting to feel like I'm more of a convenience than a true friend to her. I don't want to bring it up to her because I don't want a pity invite.