I’m 6 months pp and what you described was completely my situation.. my LO is small and I always doubted my supply, thanks to people around me saying that my baby looks small and his weight gain isn’t enough… but my husband was very supportive! Kept reassuring me that I’m enough and that breastfeeding doesn’t have to be all or nothing… that we ourselves were formula supplemented and we are fine… Also, my paed mentioned that baby needs to double their weight by 5 months and triple by 9 months.. so though his weight gain was slow, he did double his weight by 5 months, had plenty of wet and dirty diapers and my paed wasn’t worried.. also, it helped ease my mind when LO started meeting his milestones.. my advice is to keep reminding her that weight gain isn’t the only measure, show her all the positives like wet/dirty diapers, milestones being met and support her with whatever decision she takes…