OK, here's a real problem I'm not sure what to do about.

Some background: a year and a half ago, my siblings and I bought our mother
a Siamese kitten as a Christmas gift (actually, we got a gift certificate
from the breeder - my mother went and picked up the kitten later).  Her
fifteen-year-old domestic shorthair had died the previous year, and we knew
she always wanted a Siamese.  I might add at this point that I wanted to go
through a Siamese rescue, but got outvoted as my mother wanted a kitten
(both my cats are shelter babies - mixed breeds).

My mother (who, along with my father, is retired) has spoiled Molly rotten
and showers her with affection, and she's been a great pet for her but for
one problem - she bites.  Such a biter I've never seen!  She bites when
she's playful, she bites when she's tired of petting, she bites when someone
is trying to stop her from doing what she wants to do.  Not only that but
she bites HARD.  The vet recommended withdrawing all attention when she does
this, and though my mother has tried it, she still bites.  I'll add that my
mother would never dream of playing roughly with her or slapping her when
she doesn't behave.

Now, Molly is an inside cat, but the other night she slipped outside.  My
mother chased her into the neighbor's yard, fearful that she would run into
the nearby busy road.  She cornered Molly near the neighbor's garage and
scooped her up - at which point Molly went BALLISTIC.  She hissed and spat
and screamed so loudly the whole neighborhood could hear her, and to make
matters worse she started biting.  My father and my sister were shouting at
my mother to just drop her, but Mom, fearing that the panicked cat would
rush into the street, hung on, and got her hands bitten to bits for her
trouble.

Finally she dropped Molly (as she told me today, it was just too painful to
hang onto).  Molly made a beeline for the street, but when a huge truck came
thundering by she bolted into the house, up the stairs and under a spare
bed, where she stayed the rest of the night.

Meanwhile, my mother's hands were a MESS.  She takes a medication for
arthritis that makes her skin tear and bruise easily, and Molly was biting
hard enough that one of her teeth actually pierced my mother's thumbnail.  A
couple of those wounds looked as though they needed stitches, and my mother
was in a great deal of pain, but stubbornly refused to go to the doctor (she
was also crying like anything).  My sister helped her to wash the wounds and
disinfect and bandage them, and she took several painkillers (and a huge
shot of brandy, for which I can't blame her).  She was badly shaken.

My father is very upset, and is thinking seriously about sending Molly to a
Siamese Rescue.  My mother doesn't blame the cat so much, saying she was
obviously frightened, but now is very fearful of her.  Today, Molly has been
sucking up to my mother, which I think is a good sign, but I'm not sure what
the next step should be.  I was hoping for a nice, pleasant little companion
for my mother to love and spoil now that she's home all day, not a
saber-toothed tiger!  Is this something about the breed?  None of our cats
(all mutts) have ever done anything like this before.  Now that she's done
it once, will she do it again?  Is there ANY way to train a cat out of
biting besides lack of attention, which hasn't worked with this cat?  Would
sending her to a rescue be best?

Any advice is welcome.

Thanks,
Jade