[Robodog]

YES I think she was lying.

If she was telling the truth and Sam WAS playing with herself, she would have maintained her version of events when everyone questioned it, not just go all silent about it.

She's hardly a shrinking violet when it comes to sex matters, so she wouldn't have been afraid to discuss it further.

I think she lied (because she wanted to 'get at' Marc through subtly demeaning Sam), then when the group questioned it, Harry realised that she'd pushed it too far and so she decided to go all quiet and say nothing rather than back it up.