I was going to look on some Swedish emigration databases to try to help out but there were several possibilities. Also, many of our Swedes left Sweden with their patronymic name (son/daughter name, ending in son or dotter) and only later adopted a surname such as Wallin. More clues are needed.
What month and year of birth have you found for Helena on the 1900 U.S. Federal Census? What age is she in various censuses? That helps you estimate a year of birth.
What year of immigration was listed in the U.S. Federal Censuses for 1900-1910-1920-1930?
Have you found her death certificate? That should list a birthdate. Church records, lodge records, etc. often provide a birthdate. Marriage applications (not the same as the marriage certificate) often provide useful information such as the age at the time they got married, names of parents, where they were born (and often a detailed birthplace and not just Sweden) and so forth.