Curious, I don't think your baby sounds particularly underweight. My youngest is three years old and barely weighs 30 pounds! He has a good appetite, and I think he eats enough for him, he's just lanky like his daddy. My son who weighed 10 10 at birth and 24 pounds at 6 months (oh, my poor back!) was a beanpole at 2 years. And, if you can fit your behind in a baby chair, methinks your baby takes after you?
My DH is such a picky eater! Sounds like yours, actually. Forget leftovers, he balks at anything new, his ideal meal would consist of a bag of cookies and a pint of butter pecan ice cream! ( He's 5'11" and 150 pounds)
Myself, on the other hand, will eat just about everything except tomatoes, just don't like 'em, but my kids eat them like apples. I've seen them go through 5 pounds of tomatoes in a single day!
For a baby your dd's age, grazing is perfectly acceptable way to eat, as long as all her food choices are healthy. I would definately include her at mealtime, (if your hubby can't/won't eat what's before him without complaining, eat before he does so she doesn't pick up on his likes/dislikes. My Dh has had to learn to wait until the kids are in bed before starting on his nightly bag of cookies and ice cream!) Give her a little bit of food at a time so she doesn't get daunted by an amount she can't possibly eat, and add to her plate as she wants. I know I've lost my appetite when confronted with a huge plate of food!
Snacks she can walk around with are a great way to keep her fed. A nice little 1/4 slice of whole grain bread with avacado, 1/2 a rice cake with peanut butter, a bit of banana, little tidbits of healthy foods. Her stomach is only a teeny bit bigger than her fist, so look at her tiny little fist to see just how much (or little!) food she can hold in there. It's really not more than a couple of tablespoons!
One thing to remember, children will not starve themselves!