My first DS self-weaned when I was 4 1/2 months pg. Milk supply does reduce during pg, and sadly some babies/toddlers decide that the time has come. Luckily though many others go on to feed happily through the pg. At times they might not be getting much milk, but what they are getting is good for them and they still get all the other good things about breastfeeding. Wish your friend luck and suggest she just keep feeding as normal. Hopefully her lo will just go with the flow.