Bidding Question

My partner, East, opened 1H and South overcalled 1S. As West I bid 2NT which my partner raised to 3NT, which was down 2 giving us a bottom. All the other pairs were in 2, 3 or 4 hearts usually making 10 tricks. Most other Wests bid 3H, with a few doubling and one bidding 1NT. What should I have bid, and after my 2NT should my partner have rebid her hearts?