You certainly do stick to it

[shootingstar]

. . .
GEORGE:
Gee, it's funny, Emily. From my window up there I can just see your head nights when you're doing your homework over in your room.
EMILY:
Why, can you?
GEORGE:
You certainly do stick to it, Emily. I don't see how you can sit still that long. I guess you like school.
EMILY:
Well, I always feel it's something you have to go through.
. . .
(Thornton Wilder, Our Town, ACT I)

I have an issue with the word "certainly" in this sentence. What does the author want to say with "certainly" there?

 

[emsr2d2]

It's just for emphasis.

 

[Barque]

You definitely do work hard, Emily.

She absolutely does put in effort.