The PURPOSE of sr is to get a horse to work evenly into a connection, NOT for 'giving to the bit'. Ideally first the horse is in a lunge caveson, and the first contact with side reins are to the caveson. The horse works into a light connection (usually the inside is one or two wholes shorter). The purpose is very light lateral flexibility, and steady connection (ideally in trot because thehorse needs to be able to telescope/bascule with the w or c). They should be attached at the height of the rider's knee or there abouts.
IF there are too loose or esp when they are too low they act on the bars, give pain, etc. The handler first puts the horse on a small(isH) circle, puts the horse between the hand (pointed at the mouth) and the leg (whip pointed at point of hip). The horse must go forward/stay in front of the leg (aka whip touches). The fact that she backs away would say they are too low, or there is no lateral flexion. The handler SHOULD know how to properly start the horse, or have help. IF the horse rushes, go back to walk, as many times as necessary.
Do they help the horse understand a steady connection? Yes, if they are PROGRESSIVELY applied. Another good way is driving (in hand work).
The leather side reins with a donut have a small amount of give, they are certainly better than the elastic ones (because of their huge recoil action). But the handler should progressively lead the horse with them, have a helper walk on the outside while the handler lunges the horse. But any person lunging HAS to know how to drive the horse forward clearly, and that comes from other methodical work in hand first.