Seriously, we have all lost our manners these days.
This is becoming an increasing trend, married couples to be coming on with that BS comment - "oh, we've got everything, so if you want to give we want money." I have been told this at weddings and I have seen it on invites "cash gifts only please." Well, if you really have everything then why do you want my money? It is a recession ya'll, we are all strapped for cash. How dare you ASK when you really don't need. And how selfish!
OK, can we say it all together now? THIS IS TACKY! And it is totally disrespectful to your guests. Much more respectful would be to say, "Thanks, but we are blessed to have everything we need. Don't feel obligated to bring anything. Your presence to help us celebrate this day is more than enough!" Wouldn't you have felt much better if you heard that?
I don't blame you that now you and your husband don't feel like going to her reception anymore. Don't you feel like you got invited only because of your checkbook? Married couples with no taste do this all the timej -- the more you invite, the more $$$ you can get. Old tried and true trick.
I would bet you that you will also be expected to pay your own tab for drinks as well.
In displaying this disgusting level of poor etiquette, your co-worker has already brought negative vibes to her own reception. If your spirit is not in it, don't reinforce that negative energy. Give a card, without money, and give it to her at work, and then say, "I am sorry, but I won't be able to make it to your reception. Congratulations." And move on.