Ustadh Allah protect you I wanted to ask my mother wearing the hijab during Hajj is it necessary for her to cover the face with niqab or she can leave her face open because it suffocates her please advise

In iḥrām she does not wear the niqab at all. She lowers a light cloth from her head over her face, and she can try different loose covers that are open from the bottom and sees which one fits her without suffocating her. If she has a medical condition that is another story and it is for the doctors.