I arranged to see a provider next week and she has subsequently sent me an invite to join her network on LinkedIn. She is a well reviewed provider on this site and I contacted her through P411 with arrangements made through e-mail

Everyone but her is going to be guessing.
That being said, I was new to gmail and the calendar function on a smartphone and added a date to the calendar - which emailed the lady and gave her access to my friend's list.  She's a cool person so it worked out just fine.  Could the same have happened with Linkedin?  I don't use social media so this stuff is all a mystery.

I get about 3-4 of these a week. The only thing you can really do about them is to ignore them and delete them as fast as they come in.

Linkedin and other social network sites "mine" members' contacts and spam everybody in the contacts to join. The provider did not invite you. Linkedin did

I got a linkedin invitation from someone I've never heard of it before. I definitely recognized the picture though. It turns out her story was really true; she had degrees from legitimate schools and an employment history, then she lost her new job bc of a dui (keys in the ignition law apparently). I even creeped a little bit more by googling her real name and found her facebook and even the dui mugshot. Felt a little weird but it was kinda hot to see real life pics of this chick again.

I think you're right. I just read LinkedIn policies and if she gave them access to her address book, they will send an invite, and reminders, to everyone in it. I'll let her know; she's probably unaware

Who knew nothing about it.  I figured it was Linked In SPAM & just deleted it.  One more reason hobbiests & providers should keep these things separate.

What surprises me is that you haven't seen these before. Like GaGambler, I get them all the time. (frim friends, family, providers, acquaintances, - anyone who has my email in their contacts)  I just ignore and delete.

There's a setting where it will populate from your address book and invite people you might know.

Can spam generate a direct invitation? The "people you may know" is there all the time, and I sometimes get emails asking if  
I know someone. But I've never had an actual invitation that was not sent directly.

It happens just like I said. LinkedIn (and other social network sites) mine the contacts of their members and send out email invitations to people in the contacts lists.

i agree it's probably unintentional. I let the provider know.