I haven't found any restrictions on dealing with spirits, etc. I avoid magic at That Time of the Month, but pain is a good barrier to concentration, so that's nothing major there. *shrug*
I think a lot of this attitude comes from Father Church. There was serious debate up until about the 10th century or so whether or not women even had souls!!! (IMG:
style_emoticons/default/badmood.gif) Fortunately that was resolved as yes, we do. *sigh* But women are still barred from the priesthood in the Catholic Church despite being able to be clergy in the Protestant denominations, so some of this bias is still there.
I think the other half of it comes from women's duties up until modern times. Women were trapped in a pregnancy/birth/nursing/child care cycle until the advent of modern birth control. If you were one of those women lucky enough to not be able to have kids, then you also ran into legal problems as there was no one to inherit your property when you died. If you're popping out a kid every other year and raising a litter of others, only one or two of which would survive to adulthood in those days, you had no time to study magic, religion, or indeed much of anything else. Given that the life expectancy back then was only about 35, there wasn't much time to do much of anything except grow food and raise kids.
Things have changed radically in the last century and a lot of the old restrictions and taboos turned out to be nothing at all. Society has changed but the old texts date from a time when the way of life we have now would not only be utterly alien, but unimaginable given the tools they had then. So I wouldn't take the restrictions too seriously. The worst that can happen is nothing--maybe the system in question won't work for you, but then again, this forum is littered with '$magicsystem failed, should I find another' posts. People should keep trying--after all, what is magic about but pushing boundaries back and seeing what is *really* hidden in those dark corners?