I feel nauseous too after eating and if I do too much. My GERD got so bad, I had a colonoscopy and endoscopy, then saw a surgeon who noted a hiatal hernia and reflux at night that could cause aspiration and further erode my teeth. I tried all the GERD meds and nothing worked. So, I had the hernia and esophagus (wrap) surgery. They couldn't do a full wrap of my esophagus with my stomach because the sclerosis I have causes poor motility. I'm a year post surgery, have had some bouts of stomach discomfort but hadn't felt like I could throw up until I over did it doing housework. So, I pace myself now, take probiotics, digestive enzymes, and prebiotics; and everything seems to be calming down. I've been working on my gut health and liver health. I don't have to take Nexium or other similar meds anymore, but occasionally take a Tums before bed or magnesium hydroxide. The slippery elm I take definitely seems to help soothe the whole tract too.

What has her rheumatologist said about this? I suggest requesting a referral to a doctor who specializes in stomach issues (a gastroenterologist) for her.

I had the same issues and addressed it with my doctor blowing it off as a fibromyalgia flare. By the time I was able to get my Dr to pay attention and run tests I had developed ulcers in almost my entire stomach and several had ruptured and I was bleeding to dead. They ignored it some long that I was hours from bleeding out. I ended up getting a malpractice surgery that caused gastroparesis. Every time I eat it is extremely painful. If she is throwing up a lot definitely get them to run diagnostics. They made me wait so long it destroyed my upper GI. The problem with auto immune diseases is if one flares it can trigger others. I hope you are able to see if it just a side effect of the lupus or if something worse is happening

I have the same issues with vomiting it is related to lupus
everal conditions that cause vomiting:

Lupus enteritis: Inflammation of the small intestine can cause abdominal pain, nausea, and vomiting, sometimes mimicking other intestinal disorders
biologyinsights.com
biologyinsights.com
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Mesenteric vasculitis: Inflammation of blood vessels supplying the intestines can reduce blood flow, resulting in severe abdominal pain, nausea, and vomiting
klarity.health
klarity.health
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Peritonitis and ascites: Inflammation of the abdominal lining can lead to fluid buildup, abdominal tenderness, and vomiting
biologyinsights.com
biologyinsights.com
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Pancreatitis: Lupus-related or medication-induced inflammation of the pancreas can cause abdominal pain radiating to the back, nausea, and vomiting
biologyinsights.com
biologyinsights.com
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Gastroesophageal reflux disease (GERD): Weakening of esophageal muscles or inflammation can allow stomach acid to flow backward, causing heartburn and vomiting
mylupusteam.com
mylupusteam.com
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Medication-Related Causes
Many medications used to manage lupus, such as NSAIDs, corticosteroids, methotrexate, and azathioprine, can irritate the stomach, affect the liver or pancreas, and lead to nausea or vomiting
mylupusteam.com
mylupusteam.com
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. Identifying which medication is responsible may require careful monitoring and consultation with a rheumatologist.

Other Contributing Factors
Irritable bowel syndrome (IBS): While not directly caused by lupus, IBS can exacerbate digestive symptoms like bloating, constipation, diarrhea, and vomiting
mylupusteam.com
mylupusteam.com
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Peptic ulcers: These can develop due to lupus medications or infections like H. pylori, causing nausea and vomiting
Lupus Foundation of America
Lupus Foundation of America
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Management and Diagnosis
Because vomiting in lupus can stem from multiple causes, diagnosis often involves tests such as endoscopy, imaging, and blood work to determine whether the symptom is due to lupus activity, medication side effects, or another condition \

I have severe acid reflux, and I also have bad congestion and a chronic cough which is also lupus issue