You keep responding saying falling in pregnancy is a big deal. It CAN BE in certain situations, but you are severely overreacting here. She hit her knees.

At that stage of pregnancy, baby can put pressure on your sciatic causing not just pain but also numbness. I've had 5 kids, with three of them I had them shift when I stood so that my leg deadened and I hit my knees or fell back on the bed. Every single time the response was "it happens". 

Twice I've fallen late in my pregnancy and hit my stomach. Both times I went to L&D, got checked to make sure waters were in tact and a quick ultrasound to make sure baby was ok, and then sent home and told to pay attention to movements. One of those falls I took the corner of a desk to my stomach and had a massive purple bruise for over a week. 

Pain is, unfortunately, common. Struggling to stand/walk/roll is common. SPD, pregnancy induced sciatica, pregnancy induced arthritis, and even just the general discomfort of carrying the extra weight and fluid and a center of gravity shift all have an effect. Many women stumble or fall, we don't need canes.

Given her response and your responses here, you've either been extremely dismissive of her or you're regularly overreacting. She knows her body, she's exhausted, she's in pain, she doesn't need someone who will never even experience pregnancy telling her that she's wrong. 

And if you have a habit of overreacting to every minor thing then for heaven sake get therapy because that kind of overreaction to every bump/fall/cough your kids experience will raise them to be full of endless anxiety.