I have two German Shepherds and a Rottweiler right now. The shepherds were bad about not coming when called, but the Rottie will arrive promptly wherever he thinks I have a treat. There are a few things you can try..
#1 NEVER chase the dog. If it runs from you, run the opposite direction, hide and call the dog's name. Curiousity will generally get the better of her and she will try to find you.
#2 NEVER EVER scold the dog when it comes to you, even if it took 20 minutes and you are totally pissed. Coming to you should be the most pleasurable of experiences. To train her, do this: Hold a cookie (treat) where she can see it and call her "Fifi, COME".. as she starts toward you repeat in your best voice "Good girl come.. good girl come".. when she arrives, give her the treat and lots of praise. If she turns away, in a nasty, disgusted voice, "Fifi NO".. if she turns back, immediately switch back to "Good Girl Come".. You can practive this in the yard with a 12' training lead.
#3 If that fails, get a correction collar. NEVER let her know it's you doing it, but when she bolts, zap her and say "NO COME" she'll try a different direction, zap her again and "NO, COME".. when she does come, praise her and give her a treat. I had to use this method on oen of my shepherds, but only had to use it once in his entire life, and it's the only thing I ever had to shock him for (he'd run out the door, into the street, and take off). I only use a shock collar for situations that would threaten the dogs life, and I've zapped myself with it to see if it's painful. Surprising is more accurate of a description, but my hand was numb for 5 minutes..
A young dog like that is vying with you to see if she can be the boss. A method of play that will renforce your position as alpha is to gently (but firmly) put her on her back, put your body directly over hers, with your face over her throat, and talk softly and praise her. You can use one hand on each side of her head, and your elbows to deal with the front paws. Use your weight to pin her, but be careful not to hurt.. she'll act like you are killing her at first, but it's like the first year of marriage.. decising who owns the remote.. As long as she resists, firmly keep her in that position.. when she stops struggling (acknowledges you as dominant) let her up and play her favorite game as a reward for obedience.
It's exactly how an alpha dog would treat her and she instinctively knows what's happening.
Most importantly, spend about 20 minutes at least every other day teaching the dog something. Build a bond, establish yourself as her leader, and reward her for doing well. Shepherds will amaze you with their ability to retain training. You need to work with her, but she'll remember things much longer than most other breeds, so you won't need to do the same things over and over 6 days a week.
Edit: A quick tip for getting medicine into the dog, which most new owners HATE: A dog, by instinct, gorges on food as quickly as it can, because an Alpha allows it to feed for a set period. Use this instinct against the dog when trying to get a pill into it (this even works with little dogs who the owner says "Oh but she just nibbles her food all day"..
Put the pill into something she will like (I like shoving it into a cut piece of hotdog)..then cut another one just like it.. show both to the dog at the same time.. then give her the one with the pill, while holding the other up for her to see. 999 dogs out of 1000 will wolf down the first bite to get at the second one. That way, they do't bite into or chew the treat, spit the pill out, then make you shove it down their throat manually.