Is a chiropractor of any help in getting one's body back in shape right after delivering a baby?

No. Your body after delivery has a bunch of spontaneous ways to restore its condition. You can help this process with a proper diet, reasonable and focused exercise, and being a good mother. Chiropractic offers a deep massage for your spine which will have no effect on these functions even if it feels good. Discuss recovery with your obstetrician.
Yes if applied corre. 3- 4 times / week sessions for 4weeks is ok.