What About the Gas Mask?

Hi, another post here! And this post is going not that far back to 5B finale of pll. As you remember Mona got a gas Mask from -A. And we later forgot about that with all of the charles stuff:) But why would mona get a Gas Mask, if it wasn't needed? Will -A Use some weird chemical to take the girls somewhere else Because Lu tenant ( sorry if spelled wrong) Tanner, found the House and Lair!? Maybe she knows were the girls are????

https://www.youtube.com/watch?v=ylWatOaoYzA