V.W.
lemon drops
anything with ginger
stay away from caffeine (that means chocolate too)
If she is only in the first trimester, remind her to eat frequent small meals, and nibble a few saltines before getting vertical in the morning (seriously---before she sits up in the bed).
If she is beyond first trimester and is still suffering at 5 or 6 months, suggest she ask her doctor about Zofran. It's an anti-emitic anti-nausea medication that can help. It is off-label use, but it made a dramatic difference for me, and for many others.