Yes, there is that hint. It's not obvious but, as you said, it lets you infer, and then all falls in its place.
When the counselor asks for help to Hernandez, the 'lawyer', he tells him he will make one call.
Immediately after, we see Malkina on the phone talking to someone.
I believe that person is the cartel's boss, and the 'lawyer' is the lawyer of the cartel.
During that phone call, Malkina admits (reveals to us) she did call to the Texas sheriff. She says she 'just asked' the sheriff if he had found a dead body in the road (implying she put him on the track). She denies to the man on the phone she's retired; no, she's not retired (confirmation to me that she's talking to the cartel).
The conversation intensifies. She says she knows what the truck destination is, that she has always known. And when the man on the phone seemingly let's her know consequences to happen next (probably he let's her know he's got the counselor fiancée to 'pay'), she replies that falls under her "I don't give a sh!t" category (her words). She ends the phone call with "We are done", sealing the fate of the counselor and his fiancée.
Edit: hints on arranging for him to pay the fine
The hints that point to Malkina arranging for the counselor paying for his client's son ticket out of prison are a bit less clear.
First, Malkina is always listening. When the counselor meets with Reiner they both talk about security and being listened. Malkina is there.
Later we see Malkina listening to their conversation even outside that room, in the 'patio'.
After the first meeting of the counselor with Reiner, there's another hint Malkina is all over. The counselor gives the diamond to his fiancée in a fancy restaurant, and just before that the camera pans around and shows a piano playing and one of Malkina's cats right there, and a sculpture of this animals behind (so we infer it's her restaurant and she's there. Listening? Don't know.).
The next scene it's Malkina and Laura talking in the pool, Malkina watching the diamond and seeing what's it worth. I don't know if that triggered Malkina's plan, but at least we know she's quick to take action.
When Rosie Perez's character is going to meet the counselor, she makes a good look at a camera, right before entering the room where he is. To infer something, but we are not suggested explicitly anything about Malkina here. However, at the end of that meeting I believe Rosie Perez has been playing a bit with the counselor, as she is the only one in the movie who tells him he's smart, and even smiles when she asks him "would you pay that fine for me?".
Not evident, but hints.
