If she feels better in prone, take up from there. check for movement preference in sagittal & frontal plane. ask her to lie prone whenever she lies down. she can then be initiated to doing press up in the range of 10-15 degrees. If positive response is seen ask her to go further in progression of forces by achieving full range of repeated extension in lying. when ever she feeds her baby, she must not slump. she can either feed in sidelying position or raise her baby up using pillows etc & then feed. you must not forget to strengthen her core muscles as she has just delivered a baby. If she does not have a pelvic girdle dysfunction, self mobilising si joint techniques will not be of much help. do a complete assessment of SI, instead of just compression tests. I hope this will help you.