What is the ruling regarding the prayer of a pregnant woman who experiences nausea, and is it permissible for her to combine prayers, or to sit during prayer, and does her praying quickly out of fear of nausea affect her concentration?

It is not permissible to abandon prayer under any circumstances. A sick person prays according to their ability: standing, if unable then sitting, and if unable then lying on their side. The feeling of nausea does not prevent one from performing prayer nor does it invalidate it. It is permissible for a pregnant woman to combine prayers if she finds difficulty in performing each prayer at its appointed time, such as the difficulty resulting from pregnancy. As for shortening prayers, it is not permissible except when traveling. And whatever hardship, fatigue, worry, and sorrow afflicts a Muslim, Allah expiates their sins thereby.