Rebecca says she has friends who have joined LinkedIn and she's annoyed at all the invitations she gets. She also is annoyed that her email address was given to a third party without her consent. Leo says she could filter out the requests through GMail, but what she would really have to do is tell her friends to stop giving out her email address.
They likely won't stop doing that, so here's something she can try:
When giving out her gmail address to a website for example, she can add a "+" sign at the end of it followed by anything she wants. Gmail will ignore anything after that + sign, and it will still go to the same address. Then in gmail she can set up a filter to delete anything that comes to the address with the + sign attached.