The primary source of nutrition for a child up until age 1 should be breastmilk or formula. Giving solids at this age is just to get them used to eating solids. Given her slow weight gain, I would be somewhat concerned, unless this is the norm for your family. The less frequent bowel movements might also make me somewhat concerned, in particular if the foods you're feeding her are not organic. BMs are designed to remove waste and toxins from our bodies, so the longer the waste stays in our bodies the more toxins we have circulating. Also, more fruit would help to increase the BMs. And, it's important to keep in mind that at this age, one serving of food is very small (no more than 2 tbsp, as I recall), so a jar of baby food contains at least 8 tbsp. The websites for the baby food manufacturers seem to suggest far more solids earlier than what is really best for them (obviously to increase sales since it's such a tiny window in which you really need the jarred foods).
So, IMHO, if you want her to gain weight, I would actually be giving her breastmilk or formula before she eats and then the solids. The jarred baby food is just not as nutrient dense as the breastmilk or formula. And, actually at this age, if you start feeding her chunky, finger food size table food, she can eat at her own rate. My younger son did not start solids until after 9 months and he weighed 13 lbs at one month and 15 lbs at 2 months, so there really is no correlation for infants starting solids and healthy weight gain.