Hi John, welcome to IAP...!
Sad to hear such tragic event in a kid so young, broken necks normally have worse results than that but still, it will be a challenge your granddaughter (name...???) has to endure...!
Is great that you are giving her the opportunity to be creative with wood lathe and some tools, however some extra care and attention will be require with the handling and approach to pen making or any turning...!
The common safety gear is certainly a must (face mask and breading apparatus (mask of some sort), for pen making some of this equipment does not require to be as heavy duty as large turnings but still is of fundamental importance.
You may require to have a slightly wider tool rest for her pen turning as she will need to use her paralysed left hand/ in the toll rest to hold the cutting tool and for own balance. The left hand for those of us without paralyses is pretty much used as a guide for the cutting tool, the left hand (if you are right handed, obviously...!) is normally use also to assist sliding the cutting tool from left to right and vice versa but generally, the hand stand pretty much as a support.
I don't know if there is any mobility within her left arm/hand and id there is any feeling/sensation to her fingers and how the hand has "curled/locked/froze" in a "normal" to her, position as this can affect how the will need to approach the tool rest.
Despite of the lack of information to the disability, I would strongly suggest getting a protective glove for her left hand. The most efficient and obviously expensive is the steal mesh glove, similar to the ones used in the meat works to protect the hands from any cuts. There will other options that you can search/look into but, it will be important that she feel and know that her left hand that she may have no control of, is within the safest possible way while the lathe is running with whatever the material that has been turned.
The left hand on the tool rest, has to be close to the turning material to void overhang and unnecessary catches, that distance can increase sightly than most of us do use and prefer but, the safety glove will make her feel a lot more comfortable when seeing the mandrel or BTC rotated at high speed so close to the hand...!
There are many other details that can be easily overcome with the right information and attention to the needs, however these should not be a deterrent for her to be afraid of trying...! Until I know a little more about her disability, I thing this would be a good starting point...!
Good luck...!
PS: IAP would be your best place to get all the supplies you need, and you will be having a lot of us, willing to help with what we can...!
Cheers
George