Not quite understanding this?

Hello,
My daughter was diagnosed with BAV and COA (coarc of aorta) when she was 4yr old.  She had corrective surgery to repair the aorta in July of 08.  At her yearly echo the other day (she is 6 now), we were told that the aorta had some dialation... just under 2.  This was new for us.  Her cardiologist said that it is expected with BAV and there is nothing to worry about yet.  She said let's just keep our fingers crossed and hope it doesn't dialate more by her next visit next year.

Is this how it works for everyone else?  Is it really this unknown?  I'm not being sarcastic, I really just don't know.  Also, is the rate of dialation different for everyone and does it have anything to do with age?  

Thanks!
Allison