Firstly get some treats that she would die for, probably something like cooked liver, don't be mean with it, she wont return for a piece the size of your finger tip.
Start with a long training lead if you have one or a long rope, call her with plenty of excitement, if she doesn't come immediately reel her in on the lead, give her loads of excited praise and her liver treat. one she has got the message just give her the treat every other time. You really do need a very good treat for this to work, none of the shop bought treats is good enough, cooked liver can be messy but well worth the effort.