My opinion is that Mollie is nice and innocent. She likes to please others. I saw another production of The Mousetrap at another theatre recently (this is another production besides the one I directed) and I did not agree with their character choices for Mollie. She was angry and rude to people, and I don't know how that came to that conclusion at all.
This is what I think Mollie should be...
Mollie starts out a bit flustered because she's worried about the guest house. Even though she is frustrated, she still tries to be really nice and please everyone. It doesn't help when Trotter shows up. Mollie tries to stay calm, but that all is thrown out the window when she finds Boyle dead and Mollie has a bit of a breakdown in the top of Act II. The audience should always feel sympathy towards Mollie. We like Mollie. I think Mollie and Trotter are the only two characters that really shouldn't seem like suspects for the murders.
I think Mollie and Giles love each other. They have a fight because they each suspect each other of cheating, but it's because they're jealous. They love each other, so they are each hurt by the thought of the other cheating on them. At the very beginning of the play and at the very end of the play, we should see that they are in love and make a good couple.