Well, we got through the night with only one "incident" -
about fifteen minutes before my alarm was due to go off, I
was jolted awake by a blood-curdling scream from Melisande.
 By the time I got a light on and my feet uyntangled from
the blankets, whatever happened was over, and Melly was
hightailing it for the living room  (hissing a bit, but not
particularly bushy-tailed).

I had been a bit worried about the newcomer using the
litterbox (since there was evidence she'd been using the
carpet, in her old home).  She's definitely using the box
(but she doesn't cover it - fortunately, Melly does that for
her).  She seems to have chosen under the bed as her
"territory", and I didn't see hide nor hair of her this
morning, or when I got home from work this evening.
However, when I went to get myself some ice cream after
dinner, she suddenly appeared, winding around my feet and
loudly demanding to be fed NOW!!!!  (Normally my cats get
their evening meal just before I go to bed, but she wasn't
going to be put off for any reason whatsoever, and she made
that clear.)  So she got her dinner, which she attacked
enthusiastically, then headed back to the bedroom.  After
that, Melly got fed by herself, too.

A bit later in the evening, I heard a commotion, and Melly
came dashing into the living-room with an apparently angry
little bitty kitty chasing her.  (Obviously size doesn't
matter to either of them - the new girl is only half
Melisande's size.)  They're both in the living room, now,
maintaining their distance, and exchanging an occasional
growl, but it seems to be an armed truce - no attacks from
either participant.

I feel badly that Melisande seems to be the one backing down
(the new little girl may be tiny and timid, but she can
obviously be pretty feisty if she thinks it's warranted),
but I guess I have to let them work that sort of thing out
for themselves.  If the little one is the more agressive,
she is also the one without claws, so she can't hurt
Melisande, and Melly seems more inclined to retreat than to
insist upon her rights.

I've renamed her, by the way - "Cendrillon", which is the
title of a Massenet opera ("Cinderella" in English).  Most
of my cats have had operatic names, and Cinderella seemed
appropriate for a cinder-colored (black and white) cat.  (It
will probably shorten to "Cinders" or "Cindy", when we know
each other better.)