I can't view youtube videos unfortunately (slow dialup) but would comment that wobbler syndrome in the general sense of the term (mild to moderate narrowing of the spinal canal or mild to moderate subluxation of cervical vertebrae) would be at least as common a cause of EPM-type symptoms in a horse that age, as actual EPM. (Of course a strained muscle is also possible I suppose but should not produce actual hind-end incoordination if that is present)
It would be real smart to have a good vet look at the horse ASAP (and it may well involve digging into the checking account), because whether EPM or any sort of wobbler syndrome, time can be of the essence in treating, to limit damage and improve prospects.
(edited to add, after reading the following person's post since I haven't seen the video myself, another thing that comes to mind when you say "stiff neck" and "stiff uncoordinated gait" would be early tetanus symptoms, again especially in a young horse where immunity may not be solid yet. Though again, it could perfectly well be something harmless, a vet would really be a good idea, now-ish)
Best of luck to your friend and her horse,
Pat