On 9/30/2013 10:42 AM, Ivan Vegvary wrote:
Thank you doctor! I was thinking heavy in case one of her guests wants to plop his butt on top.

I am no expert, but I recently built a set of 3/4" plywood bookcases
with face frames (glued) and backs (rabbeted and screwed). The whole
frame was 3/4" ply, with all of the shelves dadoed and glued into the
uprights. The tops of my units are in no danger of being sat on (they
sit about 8' high), but they are easily strong enough.

If I were designing a 35" wide unit for the possibility of it becoming
occasional seating, I'd probably put in a middle upright as well. That
should make it strong enough for even your daughter's heftiest friends.