To be honest, strictly from an etiquette perspective, this idea presents two problems: inviting guests to a pre-wedding party when they are not also invited to the wedding, and having the mother of the bride host a shower.
Both of these things will raise some eyebrows among those who are aware of the prohibitions against each. However, from a strictly practical standpoint, it seems to have become quite popular these days not only for mothers to host their out-of-town daughters’ bridal showers but also to invite guests who cannot be accommodated at the wedding but who are close to either the bride or the bride’s family.
This is a very difficult situation, because, as the bride, you likely do not want to do anything that is against etiquette or that will offend anyone. However, as a daughter, you also likely do not want to offend or upset your mother, who has graciously offered to host a shower on your behalf. Finally, I’m sure that you do not want to be viewed as “rejecting” the love and kindness of friends of the family whose desire is to bless you by sharing some special time with you and giving you gifts even though they have not been included among your wedding guests and, due to distance, likely could not attend even if they were invited.
There are some possible solutions to this situation:
1) Instead of throwing you a bridal shower, your mother could host a tea in your honor. A tea is different from a shower in that gifts traditionally are not associated with a tea. (In truth, however, no matter WHAT an event honoring you will be called, people likely will bring you gifts.)
2) If these ladies whom your mother wishes to invite are already on-board with your mother’s ideas, one or more of THEM could choose to host the event instead. If a particular group of people (your co-workers, for example; or members of your sports league or book club, etc.) chooses to host a shower in your honor, even though the members of the group are aware that they have not been or likely will not be invited to your wedding, that is perfectly fine.
Finally, whatever happens, you don’t want to inadvertently end up violating etiquette (refusing to attend the shower, for example) in the name of trying to follow etiquette, and you, as the guest of honor, cannot be held responsible for the terms of an event for which you are neither the host nor the initiator.
I recently had some experience with a challenging situation of this nature, and I sought out and received some excellent advice from our most knowledgeable etiquette bee. She may see your post and provide her wise counsel.