Mary, thanks for the reply.  I'm Arthur's fiancee.  
My older cat, Princess, who is going through this situation, is a very
emotional (shy and scarred most of the times) cat.  She's about 5
years old (if not older).  I adopted her from a lady who claimed to
work for the local Maine Coon rescue about 4 years ago (she's nowhere
to be reached like 99.9% of the times).  At that time, the lady told
us that Princess was 1 year old.  She has always been a very shy and
scarred cat.  There was nothing we could do to bring out her cat's
personalities.  I had never asked for Princess' history as I had
always been a dog person prior to adopting Princess.  Initially,
Arthur was getting along with Princess, and in return, Princess adored
him.  That was until last year when we adopted Miyako.
Last year, a friend of ours gave us a kitten -Miyako- a pure breed
Maine Coon, whose parents' won a lot of championships in Japan.
Princess resented Miya at the beginning.  She would hide on top of the
cabinets, hissing at everybody who tried to approach her.  She was
extremely upset at Arthur, and was showing him all kinds of attitude
(this was the first time ever I heard her hissing at anybody).  But as
time goes by, both Princess and Miya get along better.  They still
don't sleep together unless we're present.  But they play together.
I don't exactly know what happened to Princess.  The "situation"
started after Princess came back from the grooming saloon.  When I
picked her up, I didn't realized that the groomer had cut (some of
)her left whiskers !!! I was extremely upset, fearing that this would
hurt Princess.  Friends told us to not worry as whiskers would grow
back.
After dropping Princess off at Arthur's place that weekend (she and
Miya have been staying at Arthur's place temporarily), the "situation"
started.  Then it stopped for 3 weeks.  Everytime I visit, I'd make
sure that I'd pay more attention to Princess than to Miya (Miya's just
more easygoing, happy-go-lucky kinda gal).  Princess displays no
problems whenever I'm around.  Last weekend was the first time that I
didn't stop by in 2 months (other weekends when I didn't stop by,
Princess managed to be fine), and the "situation" started for the
second round.  Both Arthur and I have gone back and forth to find
things that can potentially make Princess feels threatened.  We came
up with nothing.  There isn't anything new in the house, no new
perfume, no new food, no new litter.  Princess has always been a very
neat cat.  She even sits properly (with both front paws alligned at
all times).

Any help is greatly appreciated.  I know that Arthur's patience is
running a bit low due to all kinds of stress (work related, etc).
Princess had proven to be challenging, but we do love her dearly.  We
adopted Miya, hoping that the lil cat would bring out Princess'
personalities (not the other way around).  But this doesn't seem to
help either.

Thank you for your help,
Theressa

circa Sun, 06 Jun 2004 12:09:33 GMT, in rec.pets.cats.health+behav,
Laura R. (UseFirstInitialPlusRobinson@technologist.com) said,

BTW, the cat should be seen by a veterinarian.

Laura

(regretfully snipped)

Keli,
Sorry I had to snip, or my newsreader would not send.  This is really great
advice.  I believe the cat has a medical condition and/or has been seriously
abused, either during or previous to her present home. She needs constant
kindness and understanding.  I hope the O.P. follows your advice.
Annie