Hi, Ive been a stagehand for 22 years, buy her this if she likes the technical side of theater.
Go pick up the Backstage Handbook and read it cover to cover. That will give you enough basic understanding of terms and rough practices to survive overhire calls.
For familiarity go ahead and get the backstage handbook, cheap and loaded with info that's relevant to most places.
The Backstage Handbook: An Illustrated Almanac of Technical Information https://www.amazon.com/dp/0911747397/ref=cm_sw_r_cp_apa_vWn0zbJNNEVGC
Just keep in mind what previous members have said, (that whole "you've got two ears and one mouth for a reason")
That is the backstage handbook.
The Backstage Handbook: An Illustrated Almanac of Technical Information https://www.amazon.com/dp/0911747397/ref=cm_sw_r_cp_apa_i_KO6CDbSZ34KFT
Get a copy of he Backstage handbook by Paul Carter
If she wants to Stage Manage professionally you should look into a light weight headset. I just got one for my birthday and I love it. Mine is from Production Advantage, but other places sell them too. This is what I got: http://www.beltpack.com/smh710.html
Another good thing for a theatre technician is The Backstage Handbook: http://www.amazon.com/Backstage-Handbook-Illustrated-Technical-Information/dp/0911747397/ref=wl_it_dp_o?ie=UTF8&coliid=IFV9ERGDDMYE2&colid=1F2QN9CCSL803