How to prevent being overrun in the early game?
If she's in blue/green, then she has several options:

On the blue side, lean on counterspells and bounce. 4x Mana Leak will probably go into any blue deck. It's cheap (only 1U), and in the early game it's very unlikely that your opponent will have the extra 3 mana to pay to power through it. You can also run Vapor Snag to return cards to your opponent's hand (and do 1 damage!) for only U. A few of these can slow down your opponent's tempo enough to get you to your finishers.

You're also looking at cheap early creatures that can choke up the board enough to hold off your opponent's attacks for a few more turns, and hopefully provide a decent side-benefit. Here's a list of all Standard-legal green, blue, and colorless creatures with a CMC of 2 or less. Especially promising creatures for early defense include:

Oculus (chump early and get a free card)

Phantasmal Bear (a 2/2 for U)

Phantasmal Image (copy anything else on the board)

Ambush Viper (flash, deathtouch)

Viridian Emissary (trades up nicely + free land when it dies)

Memnite (free 1/1)

Necropede (great potential for a 2-for-1)

(Note that I've left several great cards like Snapcaster Mage out of this list; not because they're not good, but because their primary role is something other than early defense/control.)

The exact cards you play depend on your overall strategy, but you can certainly find something useful in this list.