She was pregnant for about 6 months. So, it will take her at least 6 months to get back on her emotional feet.
Go to her. Sit with her. Hold her hand and let her cry. Let her know its ok with you however she is. Offer to help pack the baby things up. If she says no, ask her again the next day. Her moods and emotions will change by the second. If she doesn't want to sit or talk, tell her its okay and if you can try again the next day. Then actually call her up the next day.
Offer to go to the doctor's appointment with her, if her husband can't go. Don't worry about childcare...everyone will be offering that up.
Remember her on this day next year...the 1st death anniversary of a baby is hard. Remember her on the day she found out she was pregnant, and especially remember her on her due date. Plan something special on the due date...balloon release, visit the cemetary, dedicate something to a hospital in her baby's name or light a candle.
Buy a pretty box and call it a memory box, and have her put all the baby's special things in it...sonograms, pregnancy records, special toys or clothes she bought for the baby.
When you ask her how she is doing be specific. Say "how are you doing today?" or "how are you doing this morning?".
Ask her if you can ask questions about the baby. What were they going to name him/her? Was the baby more active than her other 2? Did she crave anything different during this preganancy? Anything to help solidify her baby was real to you, because the baby will always be very real to her. Be prepared for her outbursts and please don't take it personally. Her hormones will be out of whack already...parts of her body (as well as her mind and spirit) might still be functioning as if she is still carrying a baby, not to mention her hormone levels will be up and down.
I'm so sorry for her loss.