How frequently has baby been nursing? This is very strange, that she gained 4 ounces in 2 days (which would be more than average) 2 weeks ago and since then only 2 ounces total. Weight gain is seldom steady-it would normally come in fits and starts to some degree, but that seems extreme. Scale error?
Remember that if weight gain told the whole story you would never need to bring baby in to see a doctor for a well baby check, instead there would just be baby weigh-in stations like with trucks. The doctor should (and hopefully will) assess the overall health picture. If everything else looks good there is likely little need for alarm. If supplementing is suggested and you would prefer not to do that, you can suggest alterrnatives, like seeing your IBCLC again to have breastfeeding re-assessed, and/or to have another weight check after upping nursing frequncy for a week or two, and/or start pumping again and supplement with your own milk and do another weigh in a week or two, whatever.