To paraphrase Ms. Manners, a wedding is not a date. It's an important life event for two people and whom they decide to share it with is their choice, their business.
I disagree that it is a breach of ettiquette not to encourage single guests to bring a date.
Before I was married I was invited to friends' weddings all the time as a single guest. I'm not a particularly outgoing person but I always looked forward to talking to new people, making new friends. I don't see what the problem is going alone to a wedding.
I agree, what is with the obsession on what's happening to YOU at the wedding - um, it's not about you?!
Personally, I am flattered and touched each and every time I receive a wedding invitation. To me, it says "We love you and would like to have you witness the vow of lifelong love and commitment we are going to make to each other. Please be part of our special day."
In addition, I have been 'invited' as a 'plus guest' to a couple of weddings and I declined to attend. I said to my bf "I can't go to a total stranger's wedding, it's an incredibly intimate and significant event to be witnessed by their friends and family. I'm a stranger, it would be like crashing a funeral!"
To sum up: be grateful for every wedding invitation you receive personally directed to you. It is a gift and a blessing from your friends and family, the people who love you and want you to be there to witness an incredibly significant moment in their lives.
Sneaking in guests, asking if you could 'just bring someone' as though it's a barbeque etc are all uncool in the extreme, frankly tasteless.
I have been to weddings alone and accompanied. When alone, you exercise your 'social skills'. Make conversation. Meet new people. Re-meet old acquaintances. You shouldn't need a safety-person to attend social events as an adult. It is part of growing up - take a dive out of your comfort zone, you may find you make new friends.
On the other hand, if it really makes you too uncomfortable to go alone (and from the sounds of it, this is not someone you feel particularly close to) then simply rsvp no and send a note to the bride wishing her luck.