"Use him as a bargaining chip with Laertes? Absolutely, if I asked." Possibly because he knows she wouldn't ask him for something he wouldn't be willing to give. Which is why she shan't actually bring this up with him at all... but she does so want to impress Janet, and it isn't like this is a lie. Any information she thinks Lancelot might mind getting out, of course, she shan't share. But this is a harmless fact.