What's the best way to navigate this wedding situation?

Just go. The wedding to be frank isn’t about you. Inviting mom, is the same as inviting the rest of her family. Don’t stress her out even more. You will either have this experience or not. I’m getting the notion that you’re making this about you, when it’s not really that big a deal. Stop saying to yourself, “well I didn’t get an invite therefore I’m not invited.”

I’m not criticizing you, I feel for you, I’ve been in similar situations.

It is still possible for letters to get lost in the mail. With the new machine sorting equipment it isn’t uncommon to have the machine sometimes eat a letter.

Assume your invitation got lost by the post office, it probably is true. So handle the situation as if you got the invitation.

Go if you really want to go. You got a verbal invitation, so you are invited.
If it would be easier to stay home send a nice gift. (maybe worth around $200.00) and stay put. If you didn’t send a gift they might have room to talk, but a gift with a nice congratulatory letter will make up for your absence.

If it were me and I didn’t get an invitation and knew that others did get invitations, I would not go.

Personally, I would simply double-check with my cousin. It’s not unreasonable to ask her to clarify. And I never make assumptions about anything any more.

What everyone else in the family thinks is interesting, but it’s not their wedding.

@gailcalled has it right in my opinion. Ask your cousin directly, and if money for the trip is not an issue for you and if she says you are invited, then go to the wedding. :)

Call her and explain what you’ve been told by family members but that although you do wish to help her celebrate her happy occassion that you will understand if she has a limit on the number of guest to invite and you won’t feel slighted or hurt if you were not on the list, but that you need to be sure before making flight reservations and taking time off.
I’m sure this will be something she can understand. I know what you mean. My husbands family is the same way and always thinks everyone is invited. But caterers are expensive and a list must be provided, so they know exactly how many are coming.
If however, this is an open style wedding with family bringing food or setting up the whole thing and there is no formal dinning, than I would just go. She may have only sent invites only to the elders of the families believing they will invite the rest of the family. Sometimes its just a courtesy thing for the elder folks.
Best way to tell is if your moms invite didn’t ask how many are coming or if she left it open for her to invite as many as she wishes. Meaning she wanted your mom to include family members she would bring.
Some invites may have the persons name written and an empty slash to fill for any extra guests.

With the cost, and no invite, forget about it.

Esppecially if you dont feel close to the bride.

It sounds like you don’t really want too go. I think that because you are living abroad, you have a valid reason for not attending. But as others say, buy a present and write a nice message on the card.