It's definitely worth a doctor visit.
Exophthalmos (bulging eyes, sometimes to the extent of the eyelids not being able to close) is the technical term for "bug eyes".
In young children it usually isn't anything to be concerned about for 2 reasons:
1) Baby's eyes are WAY bigger than our eyes proportionally speaking. Eyes do grow, but not much... so their eyes SEEM really big in their faces.
2) They're experimenting with muscle control, and communication. My son had an "aha!" moment, that he could get us to say "gesundheit" when he sneezed (7 of us said it all at the same time once when he sneezed) when he was 4 or 5 months old. For the next 3 months he'd do fake sneezes all the time in order to elicit the predictable gesundheit response. He'd then laugh like crazy. The reward factor of you guys laughing when she bugged her eyes out has turned it into a game. Plus it requires conscious muscle control (pulling back on her eyelids). Doing so also feels kinda weird. Add into the mix that kids eyes get like saucers whenever they're really intent/surprised/interested in something and voila... baby bug eyes.
So why is it worth a trip to the doc, when it's probably just your baby being herself? To rule out the most common medical causes of Exophthalmos. In children the most common causes are either tissue buildup behind the eyes (cellulitis, caused by an infection that's pretty easy to treat) or leukemia. ((in adults the most common medical cause is a thyroid condition, like Graves Disease. Here's a really decent picture of exophthalmos in an adult http://www.mayoclinic.com/health/medical/IM02688)) See how much white is showing above the iris? The entire eye is bugging out. If she were in profile the orb of her eye would extend beyond her eyebrow. In women, this effect is actually a sign of beauty, when it doesn't get too extreme. You'll notice many actresses and models have mild cases of exophthalmos.
Neither leukemia nor infections of the eye are caused by immunizations... and in all likelyhood... since they draw blood at well baby checkups, it's highly unlikely to be leukemia. So you're probably looking at either an infection, or just your baby girl exploring her world, one muscle group at a time. So worth a doctor visit, but no need to stress out about it.