As a long time cuckold, I would think you'd be happy she managed to get herself taken care of. Hopefully she had a great time and wants more ASAP. You two knew it was going to happen, so basically she had your permission, which she really doesn't need as a cuckoldress. My wife has never asked me permission in over 42 years, she just fucks anybody she wants any time she wants. Remember, this cuckolding thing is really all about her, not you, and as you are getting your wish, it might be very different than you thought it would be.
Most importantly, don't get upset or become jealous. The worst thing you can do is be pissed off, because she'll likely decide you can't handle her having recreational sex, and won't ever do it again because you got mad about it and she doesn't want or need the problems. If you mess this up, you'll regret it forever, and will take this mistake of unwanted anger all the way to your grave.
Don't fuck it up!