How To React To This?

Dear ILs,
I'm back with a vent! How do I react to this disgusting behaviour of co-sister ?
BIL and family stay in the US and had come down for a vacation. BIL was here for a month and co-sister and her son were here for 2and a half months and went back yesterday. So, here's the story. When they were here, we wanted to have our house warming ceremony.these people had their house warming ceremony some 7 years back, (I was not married, and hence the information contained is from all people who told their part of stories) and CS did not get any kind of co-operation from mil. Infact mil did not want her invite any of her relatives, no idea why.
My guessing is if they came, they had to be provided accommodation and transportation since none of them are from the same city. Mil is a very stingy person and hates spending for others. So CS had to call up each of her relatives and inform them about function and not invite them. CS hated this to the core, she mentioned this to me when we bought our house and told me to be prepared incase such a situation arises.
A small background about CS family- They just about able to sustain themselves , CS pays them some amount without mils knowledge. Recently when mil got to know about it she taunted CS and compared her family with mine as to well my parents are doing and don't expect anything from their daughter and all such things. She should not have discriminated I felt. However CS is 1 opportunist who will want to make the most of any situation.
She was not happy that my relatives had been invited to the function. Fact being, my parents took care of all accommodation and transportation. She was annoyed that mil was going out of her way to make all arrangements for the function, which was a great surprise for me as well. I wanted to enjoy that moment knowing it will not last long. Now, during the function, CS flicked some gift envelope which I and my family had seen. None of us mentioned about this to anyone as it would disturb the harmony in the family. We wanted to let go of it and live the moment. Days later, I indirectly mentioned to mil that 1 envelope has gone missing. For which she got offended and she has stopped talking to me. Now, this CS wants to blow this up that I am creating rift in the family, so she is adding up masala to this and trying to portray me as something else. This is the 1st part of the problem.

 

2nd part:
Since CS stays abroad, she was using my locker to keep her jewellery and I was ok with it without thinking about the consequences. I was under the impression that I'm helping her.
Last summer vacation when they were here, she took all her things from my locker saying that she now has her own locker in her place. I gave her all her things by taking her to bank so that she will be fully satisfied with her belongings. This chapter got closed last year. Now, this year, just a few hours before they leave India, she is telling me to get some of her bangles that is still in my locker. I told her, you have taken all your jewellery Last year and there is nothing left. She kept insisting that it is still there in my locker! Which is so not true! I am shocked by her behaviour. I mentioned this to DH. He scolded me saying when you know this is lady is like this, why do you even talk to her. When she brings up the topic like this, make sure I'm around so that you don't get trapped in all this. I know he will do a good job with handling this situation. But now that I have not wronged, I don't want a false blame on me. What do I do now?
I'm a very straight forward person and she is completely manipulative person, who can bluff to any extent and anyone will believe what she says.

 

She will come back only next year. Till then I can't wait!

 

Since we don't stay with ILs, she has already done her job and gone back! This time, somehow DH has got a hint of all that is happening, this is a huge relief. So now the next part is the locker stuff, which I don't know how to handle..

 

Ladies, please provide pointers on how to go about the locker stuff.. so far it is only me and DH who is aware of this issue.