(If you want something casual) DO show her that you can be discreet
No woman wants to get a reputation, especially among her friends. Reassure her that you’re not a blabbermouth. But just as in the last example, you can’t just say it directly. Try, “By the way, if we hook up later, I’m not going to tell anyone."
Instead of teasing, we’ll use storytelling in this example. Tell her about a friend of yours who hooked up with someone and then told everyone. Say how lame you thought that was, and how you value discretion and privacy.
A side benefit is you’re subtly setting expectations that you expect her to be discreet as well.
(If you want a relationship) DO get physical
Have you ever been told that if you want a relationship with a woman, that you shouldn’t try to take things physical too early? My guess is that you’ve heard this mostly from women, and it’s bad, bad advice. (No, it’s not a conspiracy–read my longer post on why women generally give bad dating advice). In reality, the man who is hooking up with a woman has a much better chance of becoming her boyfriend, if that’s what he wants and he knows what he’s doing, than the guy who is “dating and waiting.”
The grain of truth comes from the fact that some women will assume that you just want to hook up, if you’re all over her before you know anything about her. But that still doesn’t contradict what we just said.
In any case, in a friendship situation, this advice is worse than useless. You and her already know each other. Now you have to take things to the next level. So do it.