Understanding why someone may have done something unacceptable is not the same thing as agreeing that they were right to do it.
Do I understand why she did it? Probably struggling to cope and not thinking about it with a clear head or thinking about the risks. I am fairly sure that a woman who has been abandoned by a husband and left to cope alone, is probably struggling and maybe it wasn't her clearest moment. He walked away and left her to cope alone with three babies. What an arse.
Do I think it is acceptable? No. It is unacceptable for a parent to leave babies alone in the house for an hour. To go for a run. Regularly. Now, call me doom and gloom, but you cannot ensure that you do not have an accident. That's why they are called accidents.
Did she carry a note about her saying "I have left my babies alone at "? I bet not!
And what if one of them vomited and choked? Laid on its back. If you're in the house, got the baby monitor, you can rush to them. Come back an hour later and what can you do?
Same with a house fire. Nobody expects them, but they happen. Electrical faults can happen at any time. Come back from your run to find your house on fire.
Unlikely does not mean impossible.
However, since the children all made it and it's in the past, it clearly all went ok. she was lucky.
I would never say that because she happened to be lucky and nothing happened, that made it ok.
It was foolish and unthinking behaviour and yes, neglectful.