You have a good, defined voice in writing, and some of the sins I've spotted aren't unforgivable or uncorrectable. I know you're young -- I used to write like this. A lot of the difficulty is in the language; writing is about choosing specific words to convey your idea and presenting your ideas as efficiently as possible. The people who tell you, "Be careful what you share," well, I don't think anyone would want to steal this, and things go by on Yahoo! Answers faster than you can imagine.
"Day and night, she cried [produced is clunky -- producing is unemotional, a factory produces, and you're using it to describe a very emotional event, try again] -- gallons, she thought.
[Her mother should make a statement -- have a conversation revealing that it's not important to the mother. "Why you cryin', Boo?" Something that shows through your characters, instead of you, the author, stepping in and telling. It's a rule of writing: show, don't tell.] The reason for the raindrops of tears, however, was not that important as her mother had thought: Jackie, her cat, had gotten lost since Friday [had been gone since Friday ... what is today in this world?]. There were [passive voice: were, find a way to re-state it] no paw prints left for her to follow or any evidence left behind. Although Anna tried to search for the missing animal the following day [she either searched, or she didn't -- she didn't "try to search"], she still arrived in her house without a cat in her arms.
[Once, she felt she would finally find her cat -- more active] But, there was this one time she had a feeling that she was, finally, going to find her cat; instead she found herself lost somewhere: no area of the place that was not covered in green [everything bathed/covered in green -- state things positively, or else you waste words]. Everywhere her head turned, something green would be covered. [This is a restatement of what you just said.]
A house stood out to her. But, it was not any of the ordinary houses, it was also covered in green and on the roof were crows and pigeons whose eyes were amber [take your time here, but don't waste words: Among the cottages, a hard peck snatched her attention; a crow pecked at the roof of a house looming over her, draped in dark green like shadows, and in the shadows, another peck, another scrape. Her eyes darted between noises as her heart hammered. A crow glared at her with an amber eye, reflective like water.]. Upon seeing these, she thought she was having hallucinations, as she was feeling tired; consequently [consequently is a nice, big word, but it doesn't fit here], she pinched the skin of her arm. But, it did not do any good other than making herself suffer in pain [suffer is a bit much for a pinch, suffer implies length of pain, like a long time]. The house was made out of Mahogany and the window was gleaming [was made and was gleaming saps the strength out of your writing], which was eccentric [eccentric doesn't work here -- odd, out-of-place ...] due to the fact that there were many birds sitting on the roof.
Ignoring that she was seeing things [she's always seeing things if she isn't blind], she entered the front yard of the house and searched for her cat; still, no sign of meowing could be detected [could be detected -- big and clunky: She searched with eyes and ear, but neither found a cat.] by her hearing. Anna then decided to knock on the door [if she were to just walk up and knock, then she's "decided to" do so, and you could show that with action without wasted words], like any houses that seemed unusual to her. Nobody answered. The second attempt, however, did the trick.
‘Who’s there?’ demanded the voice. [Never describe dialogue in such terms -- a voice said, never demanded, exulted, any of that. The words used in the dialogue should suggest the tone.]
The voice sounded irritated and outraged. [This is good for after, "a voice said.']
Anna did not know how to respond to the voice, so, she said, ‘Hi.’ [Just having her say, "Hi," is awkward without explaining it.]
The Mahogany door flung open and an old lady appeared.
‘What do you want?’
‘I just want to—' [New paragraph, as the en-dash implies interruption.]
before she could finish her reply, the lady interrupted, [cut this]
‘Sorry, can’t help you.’
I hope that didn't seem mean, but that's hw you do it to sharpen and strengthen your prose.