Mazal tov. The correct answer is………………buy her what she would like to have. The best present for a baby is usually jewelry. That really shows appreciation and understanding because it is NOT easy to carry and deliver a baby and it deserves appreciation.
If you are NOT in the matzav of being able to afford jewelry then buy her something she would appreciate like perfume, a nice watch, something she might have been hinting about for the baby, etc.