Actually both heat and ice can help depends on the mom's preference.... Research options
http://landmarkptclinics.com/pregnancy-muscle-joint-pains-should-i-use-ice-or-heat/
Ice pack will tense the muscles up.. Heat relaxes them.
Icy hot may work
Try an ice pack n rest..Tylenol can also help
Get a handtowel wet and microwave it until its warm and put it on your back. It works a little. Not much but its better than nothing at all.
Or take tylenol or alieve.