The first thing you notice when Shayla McGruder opens the door to her downtown Miami efficiency is how young and tiny she looks. She turned 19 on Sunday, but with her girlish smile and petite 95-pound frame, she could pass for 14.

Then, sitting cross-legged on her zebra-striped bedspread, McGruder starts to tell her story, and it becomes evident she is not as fragile as she appears. She is a resourceful young lady who has largely fended for herself for quite some time. Five months ago, she was living at the Homeless Assistance Center in downtown, scrounging up change to buy a bag of chips and sleeping a lot.

“When you sleep, you don’t get hungry,’’ she explained.

The once-troubled teen is determined to turn her life around and has landed at the Royalton Apartments, a historic 1923 downtown hotel converted to affordable housing for transitioning homeless people. She is there due to the efforts of Carrfour Supportive Housing and the Chrysalis Center, two organizations that help the homeless. She is the youngest person in the building. The next youngest is 37.

Each unit has a bathroom, bed, chest of drawers, table, stove, microwave and refrigerator. McGruder decorated her apartment in safari motif, and spends most nights there alone, studying or watching mystery movies on a donated TV. She is taking five classes at Miami Dade College with the help of the school’s tutors for students with learning disabilities. She has been diagnosed with ADD, anxiety and depression.

Her holiday dream is to get a laptop computer so she won’t have to rely on campus computers and wind up walking home from school after dark. She has an interest in business administration.

“This girl’s got tremendous tenacity, and she’s going to surprise people,’’ said Carol Delaney, a clinical psychologist who has been working with McGruder. “She’s truly the little engine that could.

“Getting this apartment has been so good for her because she has control over her environment for the first time in her life. She was blowing in the wind most of her life, and even through the adversity, she has managed to piece together a little future for herself.’’

Until recently, McGruder had a tumultuous relationship with her mother, Shay Mays, a corrections officer who lives in Miramar and works in Palm Beach. Mays worked long hours when McGruder was young, so the girl had little supervision. An aunt and uncle helped when they could, but McGruder said her memories of elementary school are of coming home, “locking the door, making myself Beefaroni, and watching TV until my mom got home.’’

She got “mostly Ds and Fs’’ in school, which frustrated and infuriated Mays, who wanted her daughter to excel. McGruder ran away from home for the first time in sixth grade, afraid to show her mom her report card. She sneaked out in the middle of the night, went to a friend’s house, and hid in a closet until the next day.

When McGruder was in middle school and early high school, Mays worked the night shift, and her daughter — lonely and feeling confined by her mother’s stringent rules — regularly sneaked out to be with friends. She skipped school and got in fights (“People messed with me for being small and quiet’’). Her grades continued to suffer, and she was repeatedly suspended from Parkway Middle School, Thomas Jefferson Middle School and Miramar High.