Yeah, the timing's certainly right for Karen Kamsch, and if you read between the lines of what otherwise tight-lipped police and family members say, such as that she was being abused at the time of her disappearance (even after moving in with her grandmother to escape her father), that "she was suffering" when she vanished, or that someone in the family likely knows more than they're saying, it seems possible that she was pregnant when she went missing.
As far as school goes, some accounts state that she was in school in June of 1976, but we are also told that the school contacted her grandmother, Olga, when she didn't show for classes, and then the grandmother returned home to find her missing, with possessions including her winter coat left in her bedroom, so it seems that she was still in school. Our Carbon County Doe is supposed to have been murdered 7 to 24 hours before her remains were found on December 20th of that year, which would presumably have been about the time that students at Karen's school would have expected to have been let out for Christmas break.
On the other hand, Karen would have been 15 on January 19, 1977, so she's a little under the age range, here, and it seems that although she was (reading between the lines of various reports) possibly being sexually abused by her father, she was doing well enough in school in years prior to have skipped the sixth grade on the basis of her academic achievement, which doesn't line up well with missing teeth. Her brother, who eventually discovered that she wasn't in missing persons databases, was about 5 or 6 years younger than she, it seems. The house that used to belong to her grandmother is now occupied by her uncle and aunt. Police say that some of her relations have been forthcoming, and others have not, and they have focused on a person of interest who is either in her immediate family or very close to it. They searched a capped well in the property's back yard and found items of interest that somehow bolster the theory that she was murdered, but which do not, despite early speculation, appear to include human remains.
Karen doesn't much resemble this UID, though, beyond being female, brown-eyed, and possibly pregnant. The last information, though at her age she likely would still have been growing, puts her at about 5' 0", whereas our UID is estimated to have stood 5' 4". Karen appears to have more widely spaced eyes, a fuller mouth, and a more pronounced chin. She doesn't appear 'Mediterranean'. Betty Irene Redmond went missing from Karen's home town, Pasadena, MD, on the date of the NY Times found stuffed into the suitcases with the remains, September 26, 1976, but that makes it unlikely that she's our UID, too, since she would have had to have remained alive for several months before her murder, and since suspicion has focused on the husband who reported her missing under strange circumstances (leaving stealthily in the middle of the night with their .22 pistol, with their vehicle later located at a nearby airport), then the killer would have had to have chosen to dump her with a newspaper that would have tied his victim to that date. The newspaper seems a red herring, to me. There is a WSR radio station at Stevenson University in the Baltimore area, but again, that's likely a coincidence, just as it's likely a coincidence that two females from Pasadena went missing within a few months in 1976. I'm hoping that if Betty Irene Redmond had been very pregnant at the time of her disappearance, someone would have mentioned that and it would be on her profiles.
I see that this UID still doesn't have any rule-outs in NamUs, although there's DNA on file.