Of course it would be difficult for Rachel to use anything against L, because she was in the same predicament. L could tell any one about her strengths and weaknesses. The biggest difference between the two was that Rachel honestly felt that she had nothing to lose; where as it seemed that L had everything to lose.
Plus, all she was hearing was "Vevered, thaever im ormnorasit bla bla bla bla"
When L kissed her softly, Rachel didn't flinch. Maybe out of trust, but more than likely it was because she had dozed off by now. She had heard L mention something about Lilly being mentally stimulating, but that was about it.