Bridal Shower Etiquette

I would definitely still invite them, but tell them that there is no obligation to be there. As long as they are attending your actual wedding day then I don't think it's rude that they skip traveling for the bridal shower. You can have them appear on Facetime at some point to include them plus there's a chance they still may send you a gift from your registry in lieu of them not being able to travel. If they lived locally and skipped, then I could understand your mom's POV of thinking it's rude. But anything over 4 hours of traveling is justified in skipping the bridal shower in my opinion.

I agree with everyone else that no one can actually be "expected" to come. Each guest makes a decision about attending based on a variety of factors (prior commitments, budget, travel considerations, work schedules, relationships, etc.).

Your mom can make attendance rule for herself, but she's in the wrong if she assigns "rudeness" to people who don't attend a very optional party. I would be clear with her that she shouldn't let whether or not they attend affect her relationships with your future MIL and SIL.

As for your fiancé's aunts, I would only invite people you are close with unless your fiancé has a strong preference that you invite them and the host can accommodate them. Showers are usually much more intimate affairs than weddings and not every wedding guest needs to be invited to give additional gifts.

Your mom is incorrect. It's not rude to not make it to a pre-wedding event. Please don't allow her to colour your feelings for people. When in doubt, you can always ask here!