The Tate Modern is exhibiting a retrospective of Dora Maar. Maar’s art was obscured by her relationship with Picasso. The Dallas Museum of Art closed in February a show featuring Ida O’Keeffe. Ida had been overlooked because of her sister casting a long shadow. Back in 2013, I wrote about Paul Fontaine at the Martin Museum in Waco. In Fontaine’s case, as with many artists after their death, a...