I clicked the link in the email but it never showed up in my library. I am sure that it was my steam account that was recommended, it's been about a half hour.
There should have been a CD Key to activate the game in the email that you have to redeem
EDIT: It seems they changed that system recently to just be a link. Relaunch Steam and make sure your account is the one your friend selected when they sent the invite
they changed the way they do invites and instead sent a link and the link says the package has already been claimed, presumably by me because i already clicked the link before.
It doesn't matter if it's installed or not, it would search for the game attached to your library and force the install.
It seems if this doesn't work, the game has not been added to your account.
For the time being, your best bet is to send a reply to the email they sent you explaining the issue. Be patient as I'm sure it's not their top prio, but it should take care of it.