For an elderly with dementia and dysphagia. proned to mild aspiration pneumonia. . gets healed fast with antibiotics and oxygen. would suctioning help?

Probably not: You are describing a very difficult situation. Suctioning would at best help only a little. The mainstays of treatment include avoidance of thin liquids. Encouragement of coughing after swallowing and positional swallowing if necessary. (turning the head to one side or the other). A swallowing evaluation performed by a speech therapist trained in swallowing issues would be very helpful.

Aspiration.: Barium swallow test should be dien. See if see can change her consistency of fooed to liquid, pureed, thick, or solid food. Demented people do not chew food properly. Suction dies not hurt and you can try.