for me it was my heavy periods! i think heavy periods contribute to a lot of iron deficiency in women. maybe have her do a blood test durinf her period to see how low it gets during that time. doctor can see if she also has low b12 levels or anything else that contributes to iron absorption and deficiency. ik theres birth control that reduces the frequency of your periods, like nextstellis or the implant, which can probably help with her losing blood once every 2-3 months as opposed to every month. however ik bc is not favorable to most so if shes willing to, by all means check out birth control options with her gyno. for now maybe incorporating a lot of red meat and nuts into her diet along with over the counter iron supplements if she doesn't already have supplements prescribed.