As far as supplements or vitamins, when I was pregnant my midwife prescribed prenatal vitamins for me. I would just take her a nice selection of fruit (but maybe that's because that is what I would want someone to bring me. I like fruit:-)
Whatever you take her will be appreciated, I'm sure. She'll be pleased you cared enough to bring something.
get her some Red Raspberry Leaf tea... loose leaf is best... and some Nettles loose leaf tea too. They are perfect to drink throughout pregnancy and boost up on Vitamin K for the baby, as well as great source of nutrition. Also great when Breastfeeding. ;)