A.J.
You say she's on the bottom of the weight gain scale. Has her weight been in the same percentile consistently? I know she's only 6 weeks or so, so you may not have had enough time to get a good feel for where on the scale she'll be. A friend of mine was super stressed about her daughter's weight (because the doctor made her stressed). She's a vegitarian and was 110% committed to BF only, no formula. But the doctor made her feel like she was starving her baby. She found another doctor, more holistic and crunchy like she is, and was able to relax more. And the visually obvious thing is, both she and her husband are petite and very slender. You almost couldn't imagine a 80% percentile baby coming from them! She also told me that those charts are based on formula-fed babies. Their weight gain tends to be more than BF babies.
Good luck with the BM issue. My son had issues when he was around 1 year up until after 2 years. I looked at it like a previous poster - I only had to deal with a poopy diaper every 10 days. I could count on not getting stuck out at the store/on a plane/at the pool with a nasty diaper. But I don't have any thoughts to add for a newborn with the same issue. Good luck.