Welcome to Beyond Blue, although I must say, I am so incredibly sorry to hear of the dreadful circumstance that has brought you here. Losing someone you love is awful enough, let alone losing them to suicide.
I too lost my first brother-in-law to suicide, and have lost an unfortunate large number of friends to suicide as well. My username - soberlicious - means that I once upon a time drank a lot, and even though I am now sober, there's about 80% of the people I drank and used drugs with that didn't make it to 50 because they died by suicide.
And yeah, of course you do the best you can with what you have at the time. As you said "At the time of my decision I had the right intentions" and nobody can see around the corners. Nobody really knows what is coming next. So many people battle with thoughts of suicide all the time and so often, what they want to do is ease the pain once and for all ....... but neither you or I could ever know when that desire to just stop the pain would end in suicide. Not really. I too did what I thought was best at the time for a friend who was struggling with his drinking, and becoming abusive and dishonest, and that was to cut ties with him and try the whole 'tough love' approach ...... but he too died by suicide. Friend number 10 to die that way.
Losing focus on the present moment is a normal response to an abnormal situation; the abnormal situation being that of your mother's suicide, and the normal response being that of losing the ability to concentrate while driving. Obviously you've been driving and had your licence for some time now, and have driven without distraction before ....... but that was before there was this dreadful thing that happened and came and took over your 'normal' everyday processes and thinking. Plus, it's only been one short little month since this happened, yeah? Grief and loss, and learning to adjust to life without that person is an ongoing process. Take your time and be gentle with yourself.
You must remember this though; you did not take her life. This is not your fault. She took her own life. Forgive yourself and repeat the following for as long as it takes until you believe it; "I did the best I could with what I had."
Just take it one little bit at a time, and when driving, give yourself permission to think about and focus on the road. It's okay to have a break from self blame, you know. Take care. xo