Attitude makes a HUGE difference. Going to the party with an attitude of support and openness to learning, then letting the consultant know at the end (or the beginning, but that might make some people nervous) that you are a consultant and so won't be ordering is one thing. Going and talking trash about the consultant and attempting to keep the people around you from booking or recruiting with that consultant is just plain rude.
Understand that I would never assume that you would be rude and disrespectful in any way. If you can't adopt a truly positive attitude, though, simply decline the invitation. If you really feel a need to ask why she decided to go with another consultant, I'd suggest waiting until after her show is done. That would create less of a disruption for her and the other consultant.
Understand that I would never assume that you would be rude and disrespectful in any way. If you can't adopt a truly positive attitude, though, simply decline the invitation. If you really feel a need to ask why she decided to go with another consultant, I'd suggest waiting until after her show is done. That would create less of a disruption for her and the other consultant.