You really can't do anything. Call the doctor, if she is very dehydrated she may need to go to the hospital.
If she's throwing up water consistently she needs to go to the doctor immediately possibly even the emergency room. Go to the pharmacy and ask for the lollipops that settle nausea specifically for pregnant women. They have about three different flavored. Also, buy ensure. It's not as thick as a shake but it will cost her stomach and has a lot of essential nutrients for her and the baby. One more thing!! Syrup of Coca Cola can be ordered through your Pharmacist...I have never used it but I heard it works miracles for bad nausea. You put it over ice chips and sip! GOODLUCK