I have MS, and any vaccination will throw me into a severe MS exacerbation. We (Doctors and I) had to learn this the hard way when I had an exacerbation after a pneumonia vaccine, many moons ago (I had had less severe exacerbations after vaccines before that, but I must have hit the tipping point.) At that point my doctor and my neuro agreed, no more vaccinations.
An autoimmune disease doesn’t mean you have a low immune system, in fact, in an autoimmune disease, your own immune system is attacking your body. In MS, the immune system is attacking the myelin sheath around the nerves.
So your friend’s experience might be similar to mine, not true for all those with autoimmune disease, but each case is different.