Laura would be just fine for Smash, her sounding happy in MK8 is because that game is a family oriented game where she is constantly experiencing high speed thrills. Mercedes Rose was just the same in MKWii, and Kerri is the same in MK7.
And by extension, Kerri Kane sounds happy go lucky in Smash, since most of her clips are ripped from MK7. The more fighty ones are just from when she threw items in MK7.
Kerri Kane has grown on me a bit, since they use her best voice clips in Smash, so I'm always hearing the best of her. However, she's still my least favourite.
Also the echo has nothing to do with the actresses' talent, that's a design decision on the part of the game's sound team. It isn't Laura's fault that she doesn't have an echo in past games.