I guess since I am and Events Coordinator I must see all of this from the perspective of the Bride and Groom. If you have not planned a large event lately, especially a wedding, you may not realize the expense is now very high.
An AVERAGE wedding Reception costs the Bride and groom $100. PER Person. Many times closer to $150. This includes the venue, the food service, the cake and an open bar. Does not include anything else.
So yes, the bride and groom invited the 2 people they would love to have there and be a part of their celebration. To automatically expect them to pay $100-$150 for a person they do not know is presumptuous. Yes, many times, they bride and groom can afford this and other times, it actually helps to not have everyone be able to attend and save them that money. Think about your budgets.. Would you be willing to pay for a person you do not know? It is a very personal choice. Let them make that decision and do not assume.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It is actually considered rude and presumptuous. .
It would be putting the Bride on the spot to ask, because what a "B" she would sound like if she said "no".
Just let the bride know your husband cannot make it, so your sister is just going to drive up to keep you company. Then if the bride offers for sister to attend, great. if not that is ok too.
You do not need a date to the wedding. you are going to have a great time either way.