I was doing the recruiting for the blades after recruiting a mercenary and someone else, then I got the final recruit and fast traveled to Sky Haven Temple but my follower wasn't there.
Later I went back to Mor Khazgur (where I found her) and she was still there. I got the dialogue option to have her follow me but she said I already have a follower.
Is there a way to make followers follow when I fast travel? How can I get Mor Khazgur to follow me again?
Some times a follower will not follow if they were in combat and you left so I recommend going back and using a calming spell to calm all enemies that can not be killed so she/he can follow
If an NPC refuses to follow and says you already have a follower when you don't, and you can't fix this with a console command because you are using an XBox or PS3, you can either return to an earlier save or wait/sleep somewhere for three days, after which you should get a message that your follower has left your service. If neither option works, you can try fast-travelling a couple times to see if you are joined by a follower, after which you can dismiss the follower normally.
This is a near-duplicate of a couple other questions, You Already Have a Follower and How Do I Get Skyrim to Recognize I Don't Have a Follower Anymore. However, it's unclear whether either answer would apply in your case.
– John Laviolette May 17 '15 at 21:28