Mom's food choices should not upset her breastfed baby's tummy.
However, if mom suspects that a particular food or drink causes fussiness
or tummy symptoms in the baby, then mom can avoid that food/drink for 2 weeks and see if the baby is happier. If the baby is happier, then mom can resume that food/drink to see if the baby gets fussy again. If fussier again, then maybe there is a connection.