Mom had breast cancer and metastasis to brain, eye, lung, liver&bone. Now she felt so tired & difficulty walking. Is this the end or there is a chance?

Palliative Care. I would suggest getting in touch with a palliative care specialist. Your mom may benefit from optimizing her medications and improving her symptom and pain control. They can also help give advice for your social situation in helping taking care of her. She may benefit from inpatient or outpatient hospice. Aggressive palliative care is a way to ensure she makes the best of things.
Unfortunately. Once cancer metastasizes to brain, life span is limited. It is impossible to say how much longer she can survive, but prognosis is bleak. Sorry.