Trying to find out why service is sporadic

My mom is having trouble with her service. She's called and tried to get some help but she's not tech savvy and the reps are not taking that into consideration in communicating with her. Service is sporadic at best and has been for 3 days now. She's taken her LAN out of her router and plugged it directly into laptop. Still no service. Rep is telling her it's her router but is there some other way to check to make sure before she goes out to buy a new one? In not living with her but trying to assist her from afar. TIA for any suggestions!