I don't know if this has enough story or appeal to stand on its own.

Not really.  It might have, if you'd finished it, but ending it where
you did just isn't an ending.  In fact, it wasn't really a story, as
it had no plot.

Izuma comes very close to being an Annoying New Character (ANC).
Starting a fic with a new martial artist character coming to Nerima
is perhaps the biggest turnoff there is in Ranma fanfic.
If Izuma wasn't Ryoga's cousin, and you hadn't had the P-Chan
discussion so early, I probably would've just stopped and deleted
the story myself.

Izuma is, however, _potentially_ an interesting character, with a
few changes.  I'd suggest leaving her tall, but making her sensitive
to her appearance, which should _not_ be beautiful, but bony
and not very rounded.  Then I'd suggest toning her strength down
to between Ranma and Ryouga, rather than stronger than Ryouga (she
is a girl, after all, and females in the Ranmaverse are weaker than
equivalent males).  If you must make her capable of beating Ranma
(not a good idea for new characters, unless they are challenges-of-
the-week), I'd suggest doing it through her unusual style, which
you haven't really exploited enough.  Give her some really strange
attacks, for which Ranma is unprepared (the first time).

Additionally, is she directionally challenged?  I'd suggest not, but
give her a semi-related, and funny, handicap:  can't tell time?
can get anywhere, but can't tell anyone else how to get there?

Finally, what about her love-life?  Something very un-apropos:  falls
for Gosunkugi?

To recap, you have the germ of a very interesting character here,
so I urge you to persevere.  But she needs work.