*Notes: Interesting story. I have never read one before where the occasional transformation into another object was so accepted unless it was a story about a large group of shifters fighting to be accepted or to hide. I liked the story though. I would suggest you put spaces between your paragraphs to make them easier to read. I have included a line-by-line review below.
Red - needed changes
Blue - suggested changes and comments.
***Today, while she was finishing up her morning shower after she and changed into her clothes. (comma not a period, lower case on -i) It happened.
***Her skin started to shift, changing from human flesh to some sort of metal. (comma not a period, lower case on -c) Colored red and black. "Oh no..." (lower case on -s) She muttered to herself, (period not a comma) and (caps on -S) she looked into a body-length mirror to get a better look at herself. She had turned into Windblade, a Transformer. "Why now?... (caps on -T) thank goodness it's a weekend."
Akemi's adopted mother then found her.
***"So who are you this time? Robot samurai or something?" Akemi's mother said. asked.
***"Thanks, Akemi... and don't feel yourself too much you'll go blind that way." (comma not a period) Akemi's mother said as she left.
***Akemi just rolled her eyes. "Mom... you worry far too much about me." (comma not a period, lower case on -s) She said to herself. "Still... can I access vehicle mode?" Akemi went outside and took a deep breath. She then turned into a VTOL jet. "Yes... I can, and I intend to make the most of this." She then went flying around her neighborhood, yelling with joy at the exhilaration.
***"I turned into Windblade on Saturday. Flew around." (comma not a period) Akemi said, (period not a comma) Akemi looked around the busy schoolyard, then saw a boy. "Oh my- you think he sees me?"
***"Yeah... this has been happening for as long as I can remember. Even before I was adopted by the O'Malley's... well enough about me." (comma not a period) Akemi said awkwardly. "Why don't you tell me a little about yourself?"
***"So how was school today?" Akemi's father said asked as Akemi, with a horse torso under her human torso trudged home.
***"Exhausted... you think spending the whole day as a centaur would've helped with that," Akemi said as she fell on the couch. She then shifted back to her human self, short black hair, chocolate brown eyes, and milk-white skin, her shirt with a jacket, jeans, and boots. "You know, it's sometimes nice to be someone else. But I'm happy being me." (comma not a period, lower case on -s) She said contentedly.
***"I thought that you turn into people. You don't become them." (comma not a period) Akemi's father pointed out.