I'd take a quick trip down to West End and look around. Lots of dive shops, t-shirts everywhere, bars everywhere, and several good places to eat. Several places to stay though most if not all of the $5 variety are in the woods. Then take a ferry over the Utila and look around. I'd be shocked if you decided to return to West End. Lots of dives shops, a few interesting bars (don't miss treetanic - no place in this world like it), several good places to eat. There are plenty of $5 to $30 places to stay. Utila just has a much more authentic Honduran village atmosphere than the tourist traps on west end. You'll have a blast. If your friend comes to visit, let her talk to a few of the dive shops and for $250 or so, she can get certified too.
If you don't plan on diving at all during your extended stay, I think you'll get bored on either island but Roatan may be a better choice in that case.
As noted above I plan to dive my entire stay (or at least the majority of it) and I've already been to Roatan as well as Utila. So for me its more than a "go see it" type thinking because, well, I already have. I'm looking for ideas that'll make my 10 days seem too short.