Hi im a vegetarian and I take an iron supplement, as I was getting lots of tiredness and it did help. Im 13 weeks now so have switched from Folic acid to a general pregnancy supplement - pregnacare I think its called that has got a bit of everything.
i think there are other things apart from iron and folic acid that you're likely to need more of when pregnant, even if you're eating well - off the top of my head, calcium, vitamin e and magnesium. pregnacare doesn't suit everyone because of the type of iron in it (made me feel sick - i switched to one with a different iron source and it's fine)
I am veggie, 39 weeks pregnant and apart from Pregnacare which I started about a month before ttc have taken no other supplements. my haemoglobin level is excellent, feel great. so long as she is eating well enough, just as with meat eaters, there should be no need for anything else.