First of all, let's not use big words as "suing". Nobody is gonna sue someone for a few pics and a couple hundreds dollars. Just the cost of hiring a good lawyer ($300/h) or a even a bad lawyer ($100/h) is not worth it. Let alone the hassle of going through a trial.
Best of the worst, a mediator would be hired to solve this issue.
Second, I believe this whole experience is perfect learning for you and for the "Pro" as well. Terms should have been agreed when you asked to join him(her) on the job.
If the bride is willing to pay for your pics, you should be compensated. Now, compensation does not mean money.
In my opinion, hurting the Pro's ego will hurt your career in the industry at least as much as getting money on his(her) back. You might get a sense of that out of the tough responses of some forum members, who I assume must be wedding photographers. Be careful with this.
If I were you I would contact the Pro and tell him(her) that you have been contacted by the Bride and that she really likes your pictures (do not mention that she "prefers" your picture). Let the Pro tell you want he(she) sees the situation and the proper manner to deal with it. If he(she) has no idea, the best is for you to propose to give the Pro your photographs and let him decide if he wants to give you a few hundred bucks. 40 pics is quite a fair amount, and if it is true that you are bound by ethics, so is he(she).
If you don't get any money from the Pro, you already got experience and, most importantly, you can be sure this Pro will not "burn" you in the profession. You also should inform the Bride that you gave your photographs to the Pro for free "because it was the right things to do." She might feel bad and give you a few hundred bucks. She might not. But in any case feel free to promote yourself and let her know that she can talk about you in her entourage in order for you to get a paid job in the near future (assuming you register yourself as a wedding photographer, insurance and all good stuff).
In the end, you have nothing to lose. You went for experience, you got it. In addition, you've got good exposure with the pro photographer and you showed your talent to a Bride who may recommend you to friends/family as future customers.
Do the right thing.