Potential Brain mets – terrified

Hi, my mum is currently a metastatic melanoma patient and has just recently been diagnosed. She had melanoma on her skin that was removed about 10 years ago with no lymph nodes testing positive, however its come back now. About three months ago, she had awful leg pain and a growing tumour, after it was removed it was discovered that she had melanoma, and an MRI has shown that some of it has metastasised to the lung. Before her surgery she had a full body MRI, which showed tumours only in the lung and a few lymph nodes, however she’s had another recent MRI and pet scan to investigate if those tumours have grown/ if they’re melanoma at all. However, when we spoke to out oncologist, she said that the MRI didn’t scan the brain (which I find a bit strange), and that she needs a brain MRI which she has just had. Recently she’s had weird symptoms that she hasn’t had before. She had a spell of nausea which was accompanied by a loss of her peripheral vision, however that only lasted for a few minutes  , since then (over the period of 4 weeks) she’s had two more similar incidents, however without any sort of nausea (mainly just loss of peripheral vision). However when these happen, they only last an average of five minutes and a maximum of 10 minutes. I’m obviously now terrified that she has brain mets, and that they’re beyond cure because she’s suffering symptoms. Is this a symptom of brain mets? Do symptoms usually last longer than such a short period of time or can they be spontaneous like these? I’m wondering if her treatment options are reduced because she suffers these symptomes, even though they’re not super severe and they only last a short period of time. I’m incredibly concerned because lots of literature says that once patients suffer symptoms there’s not much that can be done. While I of course want to hear good news, I also want to hear the truth.

Thanks to anybody who has read this, I’m very distressed right now :(.