<human>: Can you provide a brief rundown of the text in within 3 sentences?

Okay so a little context here I have been dating my gf for 1.5 years now and we talk about everything. Last summer we attended a wedding of her cousin, which i'll call Shelly for this stories sake. Now Shelly and my gf are/were very close growing up and were best friends until Shelly went away for college. This is understandable as Shelly is a decent bit older.

When talking to my gf she stated that she was a little salty about the wedding itself as when they were younger Shelly promised her she would be in the bridal party due to how close they were. Come the wedding time she is told by her mom from the aunt (Shelly's mom) that there is going to be no bridal party just about S and her fiance. Normally only her family would have gone, but her younger sister was going to be on a trip to Europe so she would be more or less alone is terms of age group at the wedding. A few weeks before the wedding Shelly messages her on FB and tells her that she can bring a guest to the wedding if she would like, thats where I came in here. 

Once the wedding day itself comes and we are all seated we look up to the alter and what do you know three groomsmen and three bridesmaids. She didnt say much at the time towards it, but now has expressed her anger towards the situation to me in private. She feels like she is over it and being able to bring me was a compensation from Shelly for not having her in the bridal party. I told her I feel like she should tell Shelly how she feels/felt to get it off her chest and let her know that it wasnt right in her book and that she felt decently hurt by the lie/deceit that happened. Not saying she should atone for the actions in place, but at least apologize and talk out their feelings so there is no long term resentment from her. What do you guys think about this, am I right should she talk with Shelly, or should I drop it and allow her to be "over it" in her words?
<bot>: Gf got lied to by cousin on her wedding day by saying no bridal party when there was one, says she is okay but I think they need to talk about it still.