How concerned should I be?

My brother tested positive for COVID. He was exposed on Wednesday, and found out that the people he was around tested positive Saturday. My brother started showing symptoms yesterday such as a cough and congestion, and tested positive today. He’s been around my mom and me. My mom is very high risk. She has lupus, lung problems, (she sleeps with an oxygen tank) raynaud’s, (poor circulation related to her lupus, from what I understand) and is 60 years old. She caught the flu when I was ten, and was hospitalized with a pulmonary embolism after having the flu. She ate after my brother the other day when we assumed he wasn’t positive. Neither my mom or I are showing symptoms as of right now. How worried should I be about my mom? My mom and I are both getting tested tomorrow, to be safe.