Evidence Leslie is Ex-Military and Involved With the Tech Weapons:
She knew where the weapons were
And how they were secured
And how to operate them (at least to a degree)
She knows how to operate the comms for the two people tailing her (given that they work for the General and Waller, I suspect that they are military)
And where those comms would be
And how to spot that tail in the first place
She also handles her blaster the same way they do, and is clearly very comfortable with it
She talks like she's military. She doesn't call it a "job", she calls it an "operation".
She talks like a drill sergeant (and her outfit is eerily similar to a black version of a soldier's outfit minus the jacket)
Like seriously I've seen soldiers in that exact outfit except green not black
While being smug and talking to Wilson, whose tech she presumably JUST STOLE FROM AN ARMY BASE, she asks if he's a marine. Wilson gets PISSED at this, if you watch. It's only for a frame but his eyes narrow and he's pretty much glaring at her. For an army guy, at least based on the ones I've met over the years, that would be an insult. In other words, Leslie uses military in-jokes to insult Wilson. I would have doubted this one if it weren't for Lois specifiying it was an army base Leslie stole the tech from.
(The only thing that Leslie DOESN'T do is swear a lot. She should be dropping f-bombs every few sentences)
Slade Wilson recognizes her on sight (or his handlers have managed to identify her). Specifically, they know her by name. Assuming she's not bad at crime (which, given that she was able to steal all that stuff from, again, an EXPERIMENTAL WEAPONS RESEARCH PROGRAM ON A MILITARY BASE, I HIGHLY DOUBT), either they got INSANELY lucky, or, more likely, they have encountered her before in a context where she would have given them her full name.
Slade knows all about her history
She already has an alias/codename
That she doesn't want him to say
Evidence specifically for her being involved with thw tech weapons program: she fights with the electrical weapon like it's an extension of her body. True, she doesn't have Slade's reaction time, but she ABSOLUTELY knows how to fight effectively with the tech weapons.
That being said, Slade immediately knows how Leslie is going to fight. It takes her a few moves to figure out how Slade moves, but once she does, she IMMEDIATELY manages to take him out for a good while. So either Slade is legitimately just that good, or he has studied her fighting style. Based on the combo of that and the fact that they had a room ready to contain Leslie specifically, and I have to assume he, or someone on his team, is intimately familiar with Leslie's fighting style
Also, Slade knows how to fry her lightning suit.
And he's SMUG about it, as opposed to like. Determined or focused or any other useful emotion.
And finally, the key for me personally:
Slade assumes she will know what he means when he throws out code names, and that she is holding out on him when she doesn't answer, enough to torture her. While she clearly doesn't, he seems to think she would, and both Waller and the general seem to agree (or else why even bother interrogating her).
Conclusion: Leslie is ex-military, almost definitrly with a connection to the tech weapons program, possibly as a test subject for it. She doesn't know what Slade is talking about, so she isn't involved specifically with any of those projects, but she was clearly involved enough to know how the tech weapons would be secured, has had some serious opsec and combat training, can handle a blaster, and talks, dresses, and walks like a soldier.
