Weddingbee boards

I think it's tacky. She should have put your name on his invitation.

In answer to your first question ("is she being completely tacky?") which I am reinterpreting as "has she violated proper good manners," yes, she has. But she probably DOES think that she is following proper etiquette, because brides often get the (incorrect) advice that "etiquette says" they should address the invitation to the person they know better and use "and guest" to give that person a choice of whom to bring.

So, lest the mistake be perpetuated, what etiquette ACTUALLY says is:

1. There are no second-class guests; there are no "guests-of-guests"; they are all YOUR guests and no-one else's, and you are responsible to welcome them for their own sake. If you can't do that, or at least pretend to do that, do not invite them.
2. Every guest should be sent an invitation in his or her own name, to the address where he or she actually resides. If some poor soul is actually named "Guest", then he is the only person who should be referred to as "and Guest", and even then it should be "Mr Guest".
3. You should only invite people you know, because you are acting as a guarantor of their good character by introducing them to all your other guests. At a minimum you should arrange to meet them, or at least to receive a letter of introduction and exchange social correspondence -- both of which should give you a chance to learn their name and address.

Now, there are no etiquette police, and anyone who chooses to ignore the dictates of formal protocol because of its archaism or burdensome expectations or whatever reason, can certainly do so. Sometimes there will be no repercussions to ignoring it. Sometimes the repercussion will be that it belittles a nice person that you would like to know better, who might otherwise give you a nice gift off your registry.

Now, since there is a more-than-even chance that this girl did not know what the correct etiquette was (hands up, folks, how many of you would really go the extra mile to find out the names and addresses of all your friends potential "and-guests"?) you should probably -- guardedly -- give her the benefit of the doubt. By which I mean, let your boyfriend go to the wedding alone since you weren't invited by name, but suggest to him that he might like to reimburse you for the gift you bought and send it in his name. That's just a matter of having enough self-respect to refuse to be somebody else's nameless accessory. Skip the lingerie shower since you aren't intimate enough to be addressed by name (I don't show my undies to people I don't know by name, so I think you can assume that the bride wouldn't either and your invitation was a mistake). And then hold no grudges but be open to future chances to build a friendship with this girl should one actually evolve.