Some areas have sewer line problems where the city sewage lines are at fault, the back up happens after rain storms and can push sewage from the city lines back into residential pipes. You can call 311 to see if this is the problem, your friend’s neighborhood group might have grants to get it fixed. I received around $11,000 over two years to fix my sewer pipes and install pumps and valves to prevent the back up. My sewage line is inside, but the same may apply to your friend’s home.

https://publicworks.baltimorecity.gov/soscleanup