That would be my first guess. Allie's environment and her freedom within
it has become severely compromised by Garfield's overly controlling
behavior. There could be other existing medical problems which would
exacerbate Allie's condition.

Alopecia, or hair loss, such as you've described isn't at all normal in
cats. Check the exposed skin to see if it looks red or inflamed. If not,
watch to see if Allie has been overgrooming those areas. Because this
sounds very much like psychogenic alopecia, an OCD-like behavior wherein
the cat continually overgrooms an area due to serious and unmitigatable
stress.

Allie should still be looked at by a vet for the possibility of a
somatic, rather than external, cause. Apart from that, I strongly
recommend you either consult a feline behaviorist or psychologist or
look through materials which deal with those areas. It sounds as if
Allie's life and freedom has been suddenly and incontrovertibly
compromised by Garfield's psychological bullying, and the resulting
stress is doing her much harm. But remember: regarding the behavior and
psychology of this peculiar situation, Allie is the victim, not just the
patient. IMVHO, it's Garfield who needs behavior modification.

HTH.