Is my friend lying to me and why would she do that?

well my friend has a history of telling lies especially about dumb stuff , and she said her mum had cancer so today she must have been upset and i texted her to see what was wrong and she told me she was angry at her mum so i asked what did your mum do and she didnt want to tell me so being a good friend i am i asked if her mum started chemotherapy and my friend didn't even know what it was and after i explained it she said yes. but i shouldn't have to explain the definition if her mum is having cancer cause that is something she should know right? .So do you think shes lying to me ?