Is it just me that saw a definite similarity between the sketch and a picture of Edna Christine Thorne? Wide forehead, slim nose, somewhat long and pointy chin, eyebrow shape not far off(and it says that the UID had plucked eyebrows), and they both have a quite small mouth(or at least I think Ednas mouth would appear to be quite small when shes not smiling).
She went missing a year earlier from Pennsylvania, fits the lower age range, was probably abducted, so that could explain why shes in a completely different part of the US than where she went missing, fits the weight range(why no mention of the UIDs height?), and it says that she has brown hair in the description.
Links to Ednas case files
http://www.doenetwork.org/cases/74dfpa.html
http://www.charleyproject.org/cases/t/thorne_edna.html
I also thought Sherry Jean Pickle was worth considering.
She doesn't strike me as perfectly similar, but she has the same wide forehead and long but heart shaped face as the UID. Her eye area looks even more similar to the sketch than Edna's, even if her eyes are described as hazel instead of brown. She fits the weight range, too.
She went missing in Long Beach, California, in 1972 aged 15, which would make her
19,5 years in April 1976. Exactly in the middle of the age range. She was believed to have hitchhiked to
Los Angeles.
The fractured ankle and scar makes me think that it's not a complete possibility, though.
Links to her case files
http://www.doenetwork.org/cases/1099dfca.html
http://www.charleyproject.org/cases/p/pickle_sherry.html