Take hold of your dog's collar and hold the treat a short distance away, she will then automatically get to her feet - give the treat.  Repeat this a few times until she has the idea and as soon as her bottom leaves the floor, introduce the command "stand".

This is using the American style, if you want to use the British method, stand in front of the dog wearing the bait bag in front with a treat in your hand and step back.  She should automatically walk towards you for the treat.  Principle is the same, as soon as the bottom leaves the floor, praise and treat.

You can also walk towards your dog to encourage them to walk backwards - if your dog has been taught to sit, you may find this is the natural reaction.  Continue with the exercise withholding the treat (or click) until you get a walk backwards.  Alternatively work out a situation where your dog has to move backwards e.g. if you stand with your legs apart and put a treat on the floor past your legs, the dog will walk forward to get the treat but has to walk backwards to make eye contact with you.  As soon as the dog walks backwards, click or use your cue word.

You can then either encourage your dog to walk into position:

Or manually place the dogs legs (more photos of this to follow - we ran out of daylight!).  When positioning your dog's legs, always use the same hand (e.g. move legs with the right, feed with the left).  Once your dog is positioned you need to introduce the "stay" command.