But other than needing to be weeded of adjectives, this is quite nice. I'd like to know who she is, and how old. I experience entirely different responses to the piece if I think she is 6 years old, versus 26 or 96. Is she lost and looking for something, or just lost with nowhere to go?

> Walking the cold, cobblestone streets

Nit: I'd say you don't need a comma here. They are
cobblestone streets that are cold; not streets that are
cobblestone, and also cold.

> of London, with her numb, cold feet,

This is the second "adjective, adjective noun" formulation
in this sentence so far. Not always bad, but something to
notice and perhaps change. (E.g., do her feet have to be
both numb and cold, or can they just be cold?)

> she turned the corner.

What corner? Why is this corner, the site of the first
action she has taken in the story, so important?

You don't answer, and then you talk about her frock.

> The harsh bitter wind sliced through her thin, tattered
> frock,

The "adjective adjective noun" sliced through her
"adjective, adjective noun",

> Long had she been lost,

Archaic / poetic sounding. Okay if that's what you're
looking for, not if you're not.

> wandering among the many maze-like streets of London.

I'd kill the word "many", which distracts from "maze-like"
but doesn't significantly add to the description of the
streets of London.

Also, this is the second time you've said "streets of
London" in the last three sentences, which was definitely
(to me, anyway) an ear-catcher.

> “Portabello Road” she whispered, staring at the
adjective adjective noun.

In general, you've avoided the passive voice, which is good and
indicates less need for condensation. I think you might need
more variety.

"Trying to fight" can almost always be replaced with
"fighting". Same with lots of "trying to..." locutions.

I'd describe the street sign first, as she sees it, rather
than waiting for the next paragraph.

Unless the road itself is a major feature of the story
(which it might be, given the title ), I wouldn't have
her repeat the road name right after you provide it to the
reader in narrative summary.

You need punctuation after a character's statement, e.g.,
'"Portabello Road," she whispered.' (Note the comma after
"Road".)

This is a nit, but you have her looking up and saying
something, both small movements; then you have her following
a twisted alley, which is complex. That's not necessarily
wrong, but I would examine it to see if you can communicate
this better.

Here are a few practical application of my criticism.
(They're only two of many possible alternatives, and Oliver-
ish ones at that. Also, they're written by somebody who
doesn't know what's going on, so you should probably throw
it away and try your own.)

----
The wind sliced through her tattered frock as she turned the
corner of the London street. It was like any of the others
along which she had wandered -- one more corridor in a maze
designed to chill her bones and sap her spirit.

She looked up, pulling her twig-thin arms tighter around
herself, fighting the abrasive winter air. The street sign's
red paint was chipped but legible. It read, "Portabello
Road."

"Portabello Road," she whispered. A twisting alley opened
before her, filled with shops, merchants, and food carts.
She stepped into it, apprehension [or joy, or sadness, or
whatever doing whatever it does to lead to the first full
scene...]
-----

I think that's better, although there are still too many
parallel prepositional phrases in the first sentence. Maybe:

-----
The wind sliced through her tattered frock. She turned
another corner -- one more twist in the maze that was London
-- and pulled her twig-thin arms tighter around herself,
fighting the abrasive winter air. The street sign's red
paint was chipped but legible: "Portabello Road".

"Portabello Road," she whispered. A twisting alley.....
-----

Original: 71 words.
Final: 46 words.
Cut factor: 35%-ish.

I still don't know what this waif is doing in public at this
hour. Hopefully you'll explain soon.

Regards,
Oliver