High Calorie and Fat Content Baby Food (To Make Yourself)....

"Mommy Made (and Daddy too!)" is a great, low-key baby food recipe/preparation cookbook to pass on to your SIL. It also has a great, general (but flexible) schedule for introducing different fruits, veggies, and meats - for someone feeling less confident about making your own baby food (easier AND cheaper!) it could be a great resource. Honestly, though, for the first year, breast milk or formula should be her main source of calories. Solid food at nine months should still be "practice" for swallowing and chewing and experiencing new flavors.

I understand the desire to see a big, chunky baby, but not all babies are like that. If she's eating well, pooping well, and her doc says she's doing well, then trust that she's the weight that she should be. My best friend and I had babies six weeks apart, we both breastfed, we both had great eaters/sleepers who, when we added solids, ate a wonderful variety of (homemade) foods, and were very physically active - and until they were 3, her daughter outweighed my son by 3-7 pounds (and that's a big difference on those tiny bodies.) My son was a skinny little bird-boy, and her daughter was a roly-poly chunk. Kids are just built differently, that's all. Our kids are now seven, and my son is tall and muscular and strong and solid (though still skinny) and her daughter is tall and muscular and strong and skinny (though still solid.)

I applaud your desire to help your SIL make her own baby food, but don't worry too much about the munchkin. She's on her own growth path, and she'll get to where her body needs to be.

Do pumpkin. You can buuy it canned or do it yourself.

Oh yes - avocado is a perfect baby food, full of good fats and calories. The other best way to add fats and calories is to saute all the baby veggies in olive oil, or even add butter or coconut milk. I had two tiny babies and we added olive oil or butter to all of our baby foods. When they got a little older I mixed coconut milk into all the fruits.

I would also suggest avocado and bananas. You can now add in dairy products (not milk though) as well now that she's 9 months.

Some more advice here:
http://www.livestrong.com/article/241766-high-calorie-foo...

My daughter gained weight after some non-weight gain by eating avacado (guacamole, actually!) and then sunflower seed butter (at one year). She also loved yams, which are easy to cook and pack a much more nutritional punch than potatoes or sweet potatoes.