There are a few unidentified cases from Washington, DC, that could be Helen:
#UP16571-Female, White/Caucasian, found in 2005. Estimated age 40–50, height 5'3" (same as Helen). Estimated year of death is 2002–2005, which would make Helen about 46–49 if it’s her. The age and height are an exact match, so I think this is the most likely option.
#UP87267-Female, White/Caucasian, found in 2001. Estimated age 25–35, skull only, estimated year of death around 1991. Helen would have been about 35 then, so it’s possible but less likely due to the lower age range.
#UP59378-Female, uncertain race, found in 2010. Estimated age 18–50, height 5'0"–5'4". The age and height ranges are broad, so there’s a chance, but not as strong a match as the others.