Over two years for a sketch book?

[iluvhistory.livejournal.com]

I commissioned an artist in 2005 for a 100 page sketchbook, we fell out of contact but she has it listed on her page as halfway done since last winter. This is a bit strange to me since when I commissioned her she never mentioned that it would take several years for it to get finished. Four years total (since she was halfway two years after I commissioned her) would imply one page every two weeks or so.
Does this seem like a reasonable pace for a sketchbook commission?

I don't want to seem overbearing since that would imply one page for every two weeks and she has work outside of art, as well as school, and having some genuine hard times. At the same time I don't want to wait forever and never see what I paid for out of an excessive amount of caring. She checks up to see if I've changed anything on my characters every six months or so, so it isn't like she has disappeared from the face of the earth.

What would be the best way to approach asking for an estimate on when the sketchbook would be completed without sounding hostile?