Didn't she tell the waitress that she was 19 though? And waitress didn't think she was that old? That would only be one year off her true age if this could be her. I wouldn't rule out based on the age someone 'looks' as my 27 year old daughter looks about 16 and gets ID'd every time she goes into the liquor store or when she orders a drink with us at a restaurant (legal drinking age here is 19).
Age has been revised to 14-18, but nothing mentionned of child birth. Are we certain that Sherry had a child - the missing poster doesn't mention that nor does her NAMUS profile. There's a photo of her holding a baby in her lap, but I don't think that infers the child was hers; looks like she's sitting in a backyard.
And correction NAMUS states Sherry was 17 when she went missing so she still falls within the new NAMUS age range of 14-18.
91UFTX (doenetwork.org)
A few pages back, I was absolutely thinking the same as you, but Carl confirmed that Sherry's child had been in contact with him for his help
Missing Person Case (namus.gov)