Wow, what a conundrum. Such a lovely opportunity to attend a wedding as a woman (one of the things we all dream of doing, if not being the actual bride), but your wife apparently doesn’t know so you’re not sure how to broach the subject. Well, my first question is, how open and honest are you with your wife about other things in your marriage? If you’re not, then starting with the topic of your being a crossdresser might not be the best way to start opening up to her about things. But if she does know about everything else, then maybe, as has already been suggested, it’s time for the talk. You could explain your history, how long you’ve been crossdressing, why you kept it from her, etc. and then see how she reacts and then make a decision. Of course, you’d also have to tell her how another woman knows about Lisa and she doesn’t, which might be awkward.
My best suggestion is to pass this time around, then talk to your wife, and then perhaps another opportunity may come along and you can both go together. Just think how much fun it would be to shop for dresses with your wife so you can both attend a wedding! Now that would be something to really look forward to!
Good luck and be sure and let us all know how it turns out.