Upload & Sell: On
It makes perfect sense for a competent wedding planner to want to see vendor agreements. Here's a great opportunity to network with someone who has a greater ability to steer business your way than do most other people.
So, you could treat the planner in a condescending manner and put her off, or you could communicate professionally, have a friendly chat, be firm in your terms, and then have a useful contact.
There's a possibility that the planner has other photographers in mind to whom she likes to steer business, and finding "problems" with your agreement (or your refusal to negotiate) will be her pretext for undermining your relationship with the couple. So it may be valuable to have the client on the phone when you speak with the planner until the contract is signed, so that the client can see how reasonable you are in responding to the planner's questions and challenges. The one thing you must avoid is allowing the planner to misrepresent your stance to the client in an effort to portray herself as fighting for them. And if she has set herself up as their "advocate," putting you in a newly adversarial position, then having the client on the phone during negotiations is vital to protecting your relationship.