Ok, we hit the standard barrier that is probably very common. Our 16 week old GSP has the basic obedience down very good. (notice I did not say 100%) Come, sit, stay, heel, down. I have noticed lateley that she now knows when we want her to come for a reason. Like she wants to visit the neighbors 2 labs, or she just wants to stay outside. When I start walking towards her, she already knows and is laughing hysterically to herself. So what if food is not more enticing than checking out her pals?
You are missing the point with the come command. It means come every time no exceptions, not because there is some reward at the end. So, put her on a leash and start training the come on leash so you are in control. Put her in a sit stay and walk to the end out your leash. If she gets up, go put here back in the sit stay. When you get to the end of the leash tell her to come. If she just sits give her a little tug to get her moving, as soon as she moves in your direction praise and get all excited. Now if you are teaching for obedience competition you will want to end the come with a sit right in front of you. Then more praise and a treat of play or whatever. Do NOT train come off leash until you have a 100% reliable on leash come. Do not add distractions until you are 100% reliable as well. Progress this slowly and you will get to a reliable recall. If you are not training for obedience, then you can reward her when she gets to you. There is another thread that talks about a reliable recall. So, do a search and you will find allot more details. Also, if you have questions, just ask.