I understand how it can feel like that. But I honestly, hand on heart, think that its a question of perception.
In the situation you cite here, you have no way of knowing for certain why she decided to prioritise the other child over your child. There are all sorts of factors you may not have been aware of: the other child's family could have been in crisis, they could have lived closer, it could be that neither of the parents drove. It could honestly have been the child's preference.
It's possible that in some situations this is an act of social engineering but I really think most of the time busy mums don't have the bandwidth or the energy to do this.
Also, as an associated issue, I think your reaction of saying "I know my place" is really unhelpful for you: because you're automatically setting yourself up as being seen to be socially inferior. Again, I can't know for sure that this isn't true but I highly doubt it. But by accepting this perception you are automatically casting yourself in this role.
If you want people to move past this perception, you have to shrug it off. If you fall into this "I know my place" perception you're not only ensuring that people will treat you in an inferior way, you're setting your kids up to have the same self perception.
If you think someone is dissing you or ghosting you, just move on from it, cut them out and don't give them a second thought if you have to. Do whatever you have to do. But don't keep telling yourself you're inferior. You're more or less inviting them to think the same thing.