Hi, sorry for your loss. Your mother could be going through grief reaction. A period of emotional unrest after losing a loved one is normal. If your mother is unable to cope with it I would suggest seek consultation with a counsellor/Psychologist.
Next Steps
Most likely the chest pain is due to the emotional stress and may not be anything serious. However in women severe emotional stress can trigger certain types of heart issues, so parallely get a physical evaluation and ECG with Echo done.