Is a pregnant woman's prayer invalidated or its reward diminished if she completes it sitting due to nausea caused by standing and bowing?

Standing in prayer is a pillar, but if a worshiper is unable to stand throughout it or for part of it, it is permissible for him to pray sitting, and his prayer is valid, and his reward is complete; because Allah Almighty says: "Allah does not burden a soul beyond its capacity" and His saying: "and [He] has not placed upon you in the religion any difficulty." However, if one prays supererogatory prayers sitting without an excuse, his reward is decreased.