Is what the questioner did correct regarding completing her prayer and disregarding light bloody discharge and brownish discharge after seeing dryness, and her saying that she relied on the hadith, “We used not to consider yellowish or brownish discharge after purification to be anything,” and her husband having intercourse with her?

If what you saw after the signs of dryness was a light yellow (sufrah) or brownish (kudrah) discharge, then ignoring it was correct, because it is not considered menstruation after purity if it occurs outside the usual period and is not connected to blood. However, if it was explicit blood, then what was done was an error, because in this case the woman reverts to being in menses. She should have refrained from prayer and marital intimacy until she performed ghusl (definition) (ritual bath), and she must make up the prayers she performed without having bathed. There is no expiation due upon her for her ignorance of the ruling.