A.C.
Prunes won't hurt. :) You can up her fiber intake (prune or pear juice, prunes, whole wheat bread/bagels/pasta, etc.) and it won't hurt her (though it might make the poops bigger in amount).
Don't feel selfish--imagine if you woke up in the morning, earlier than normal and woke up feeling like you needed to go--not the most comfortable feeling in the world, no doubt!
I would say to try shifting her dinner later in the evening, or earlier in the evening, and see what happens. I also suggest changing to 5 or 6 mini=meals per day (which might actually be better for you anyway, being pregnant)--for each, try to include a protein, and a fruit or veggie, or a carb and a dairy, etc. That might also help change her body's processing.