Fenugreek, fennel, anise are my suggestions. I used them and had some succes. I remember also making carraway tea to increase my milk supply.
The most important although is that the breastfeeding mom is not under stress. If I were her I would put the baby on the breast every 3-4 hours to stimulate milk production + would pump to get more help.
Hopefully she eats well and drinks enough water. Dehydration is another factor for not getting enough milk.
Wishing her luck and patience with it.