At 4 months she should be getting a bit better, but you will need to do lots of work in the middle trimester to prevent the problem recurring +++ in the final trimester.
one of the common problems is anterior rotation of the Ilia (usually one or the other not both) with increasing lordosis and abdominal size. If this is present, you must correct it and keep bothSIJs mobile or she will get PS problems which are very difficult to treat. regular DT work to piriformis will help. exercises to increase core stability esp TA, lumbo-pelvic flexion (ie cat exercise) to decrease lordosis, lots of fit-ball work and aquatic exercise but avoiding end of range asymmetrical hip movements. belts and tubigrip L are very helpful but only if the pelvis is in a good position before they are put on.Good luck, you can also tell her that about 85% of the pain will go as soon as the baby is born!!