My mum has idc breast ca. primary lump in left breast, axillary nodes, both left&right supraclavicular nodes involvement. is this stage 4?

Yes/Early stage-4: Spread of tumor into supraclavicular nodes makes it inoperable which males it stage 4(when you add the opposite supracalviculatr nodes. Yet it is early phase of stage -4. Therefore, if treated properly by an experienced breast cancer specialist(medical oncologist), it can be controlled and may even be cured if luck works in her favor.