The honest answer is that you cannot make an adult accept help, and trying usually costs you the access you still have. So the aim is to stay close enough that she comes to you when she is ready.
A few things that tend to work better than persuasion. Ask about specifics rather than the whole: how she slept, whether she ate today, not whether she is depressed. Specific questions are answerable; large ones invite "I am fine." Offer a concrete, low-cost option rather than a decision: the free ten-minute call exists partly for this, because it asks almost nothing of her.
Also worth saying plainly: two months of withdrawal with disturbed sleep is worth a medical appointment as well, not only a counselling one. Some of what looks like low mood has a physical contributor, and it is cheap to rule out.
If she will not come, you can come yourself. Working on how you respond is not second best; it often changes the household enough that she moves.
This is general information in reply to a public question, not advice about your own situation, and it does not create a client relationship. If you are in immediate danger, contact emergency services.
