That is exactly what I was going to suggest, using the SNS or LactAid to give formula at the breast. It might stimulate you to produce more and you'd know that she's getting as much breastmilk as you have without having to stress over pumping. You have made so many sacrifices and worked so hard to breastfeed and this is totally not something that is your fault. You have to do what works for you and your family, whatever that may be.