Does a sister's not having been committed to prayer before her marriage affect the acceptance of the Istikhara prayer she performed when a suitor proposed to her, and does this therefore mean that her current marriage is not good, after her discovery of some of the husband's flaws?

This does not indicate that the prayer (Salah) or Istikhara was not accepted, for indeed, the supplication (Du'a) of even the wicked may be answered. The presence of flaws in the husband does not negate the existence of goodness or virtuous character in him, as perfection is not found in human beings. The wife should be patient, as long as she is not suffering clear harm, and strive to remedy her husband's flaws through sincere advice and supplication, knowing that abandoning prayer is a far greater danger.