That was studying wild Hemp, not domesticated cannabis.
In 1930s, the concept of hybrid cannabis was probably not even thought of....and majority of the strains today are technically, hybrids.
That said, she did pop cannabis sativa beans and the results she got are probably more reflective to the cannabis we use today--than say the results and conclusions of studies/research on "non-cannabis" plants, like tomatoes.
But it is interesting the mineral deficiencies she observed are accurate for today's hybrids.