78 kph/48 mph isn't that fast honestly, I think the biggest problem was that she was fucking wasted. If you can't keep your shit together at 50 miles an hour you probably shouldn't be driving.
Okay, so the limit was 50km/h which means she was in a residential street driving at a speed that is reserved for highways. It definitely matters and is more than fast enough. She fucking killed someone.
The fact you're converting to mph makes me think you might not be familiar with speed laws in Australia and what the expected traffic speed is on the average street.
35m stopping distance is quoted for 50km/h. 78 km/h is 65m, or 10 car lengths. from the standard calculator, which assumes normal, non inebriated reactions. This bloke is cooked.