Depression is horrible to experience. I have experienced it for quite some time with the worst being a couple of years ago and the episode lasted for about a year. I was admitted to hospital on many occasions for self harm and overdose. I was a mess. I lost so much interest in the things I once loved. I saw psychiatrists and cognitive behavioural therapists. Medicine makes me groggy and put on weight and I do not like talk therapy. I could never really express how I was feeling.
There are many causes of depression - including chemical and reactive. My depression is caused by a combination. Looking back, I can see that I felt hugely inadequate at the time. I felt I was not living up to what I should be or wanted to be. I felt not worthy.
There could be numerous reasons for your mum's depression. At this stage estrogen levels begin to decrease. Is it possible to have hormone replacement? I am not sure - has she spoken to her Dr about this?
This is a period of huge change in her body, life, and how she perceives herself. I would assume that she too would need to know that she is worthy of love and is appreciated. She may need to feel more comfortable in the role that she has now as an older (54 to me is not old at all - but she may feel this) lady or perhaps grandmother.
Please research the medicine she is taking. Many have terrible side-effects and are really difficult to come off.
Perhaps get her interested in something else such as yoga, a walking club, a gardening club, line dancing? Maybe she is tired of her usual interests as they remind her of a time and place that she can not re-connect with again? Sorry for the babble, hope this is of some help.