CREATE TABLE table_204_553 (id DECIMAL, "outcome" TEXT, "no." DECIMAL, "date" TEXT, "tournament" TEXT, "surface" TEXT, "partner" TEXT, "opponents in the final" TEXT, "score in the final" TEXT)

which parter did she have the most ?
SELECT "partner" FROM table_204_553 GROUP BY "partner" ORDER BY COUNT(*) DESC LIMIT 1
SELECT "partner" FROM "table_204_553" GROUP BY "partner" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1