I'm involved with a large portion of Brides to be, around 7000. This may sound harsh, but, for the most part their budgets are blown out of proportion before they know it. Catering is expensive, venues charge per person, food per person, drink per person. You invite a single person and they before RSVP, ask " Can such and such accompany me?". It's a nightmare for the Brides to be, or "My children have to come".. When it stipulates "no children". Cutting costs for weddings is difficult. In some instances, single people are invited deliberately as they are someone that the Bride would love to be there, however, they figure, that the person would turn the invite down because they have a partner and if the partner isn't invited, they won't go. This helps the Bride with numbers and with not offending anyone.
I know of no Bride that has invited a person without their partner "wife". So I would say she is expecting you to say "no". Same for the other lady, if you are not there, she won't want to mingle on her own in amongst a bunch of partners.
Taking that aside. You need to re-read what you wrote because you need to help your wife feel that you two are a couple, she is important, there would never be anyone else.
This is one small step to show that to her.
After all she's worth more than this co-worker right?