Reverse driving accident. Who’s to blame?

Good day, and I have the following problem. My mother drove her car from a front road (30 zone / right in front of left) backwards onto a main road. Has looked around before she left of course and when no car came backwards on it. A car came on the main road and wanted to turn right and drive my mother behind on the bumper. Who is now to blame? I have heard this when someone is going backwards usually always blamed Is that true? Especially since my mother comes from the front road… can you help me there further? LG Wayne93