Well, she apparently killed that creep who implied he was going to rape her in the alley when she stumbled out of the hospital after waking up from her coma. The audience knows that was probably some variation of accidental (she didn't know about her powers yet) or self defense, but without witnesses, it looks like her first kill.

We also don't know how bad the DEO agents who responded to her breakout in "World's Finest" were hurt.

Leslie did, however, as you point out attempt murder of Cat, Kara, Barry, the helicopter crew and she was warming up to "thin the herd" of bystanders at the park. Which is a clear threat to indulge in mass murder.

So Kara may be exaggerating about how lethal Leslie has been so far, but not about her intentions.

Well, she doesn't bring daisies....

Okay so she has body count of 1
(And it could be argued that it was in self defense) Remember Alex has a body count of at least 2.

As far as thinning the herd if she actually wanted to kill people she would have directed her sparks at the crowd, not the ground. I assumed that she was simply trying to scare them away first. Then if that didn't work, she would kill them. So yes she was willing to kill them but not eager to kill them, and had they not gotten in her way she probably never would have threatened them at all

As far as I can tell attacking the helicopter was the only attack not related to achieving her goal of killing Cat and Supergirl or fending off a rapist.

It still doesn't seem like much compared to other villains, like indigo who tried to nuke the city and Maxwell Lord who
planted bombs and created Bizarro and red kryptonite.

In terms of people in general she's a bit violent. But when you compare her to other supervillians shes not so bad. Certainty not bad enough to panic over, and she has a weakness that is really easy to exploit that for some reason Kara never bothers to do.

I think Leslie's weaknesees are kind of overstated because ...

well, water.

But we saw the other characters given her powers "teleport/wire-ride" away from a spray of water at a second's notice. As she gets more experience, and gets her emotions under control so she can pay attention to her surroundings, that's going to get to be about as hard to use on her as Kryptonite is on Kara and Kal.

"But we saw the other characters given her powers "teleport/wire-ride" away from a spray of water at a second's notice...."

A spray of water won't defeat Livewire (or another character with her powers). In order to be totally short-circuited, she needs to be doused (or drenched) in it.