You're right that she looks younger in the sketch than what you'd think for her age bracket + possible lifestyles. Regardless of her situation, her body is very underweight with a BMI of 16.5. It's difficult to know what caused this (homelessness, addiction, or an eating disorder). It would be very interesting to see the state of the clothes she was wearing, as her layering clothes could have been because she was wearing all her possessions, OR because it was December and cold out for someone so thin. You're right that it's hard to tell the state of her life from the picture/body info that we have. For all we know (given the information) she could have been a young professional abducted during a jog & taken across state lines.
As for other marks on the body being indicators of drug use: being a drug addict doesn't necessarily require marks (like injection scars) on the body. Addiction can also be reliance on opioids in pill form, some of which are made from illegal pill pressing operations (and are oftentimes laced with highly potent & cheaply sourced black market fentanyl). I received Narcan training for my job and learned a lot about local Philly drug tendencies from this amazing overdose prevention officer named Elvis Rosado. It's all pretty terrifying.
Fentanyl vs. Heroin: The Similarities and Differences Between Two Powerful Opioids