Only three miniatures by Roberts were currently known to exist until fairly recently; none is signed with her full name, but each is inscribed "MR". All are undated, but based on the styles of the clothing and wigs depicted are believed to date from the 1740s. The technique is assured enough to suggest that Roberts had some sort of formal training in painting prior to arriving in Charleston. At least one of the portraits, a watercolor on ivory rendering of a Woman of the Gibbes or Shoolbred Family, still exists in its original frame of gold set with garnets. This work descended through the Gibbes and Shoolbred families before coming to the Gibbes Museum of Art.[1]
In 2006, five watercolor on ivory miniatures of children, a group of cousins from the Middleton family, were found at Shrublands (the family estate in England) and purchased by the Metropolitan Museum of Art in 2007. Each one measures 1 1/2 x 1 in. (3.8 x 2.5 cm) and is in its original gold case and signed MR and was painted around 1752 -1758.[4] The portrait of Henrietta Middleton is on display at the museum.[5]