EEs are defined as any chicken that has some form of the blue egg gene, but doesn't fit an APA standard... so EEs could potentially lay pretty much any color of blue or green.
When she first starts laying, there might be some minor color change, but for the most part, your pullet will always lay the same color. When a hen ages or experiences some stress or illness, the egg laying process can be disrupted and cause changes in the egg.
If she has a pea type comb, she is much more likely to have the gene for blue eggs, but given the mixed ancestry of most EEs, it is never 100% sure. Green eggs are produced when a brown coating is added toward the end of the egg production cycle, making the eggs look green (but you can see that the shell is still blue on the inside). This is the same for brown eggs, which are actually white shells with a brown coating.
Since many breeds with red earlobes are brown layers (and white earlobes, white layers) you might look at her earlobes to see if she is more likely to have the brown coating. This is not 100% either, but is something I've been curious about, has been true so far for 6 EEs in my little survey!