Lulu:
She doesn't talk too much with people (she ignores them sometimes), she is clever but she's a temp, she does everything she can for money because she needs them, but she is a good person. She takes care of the people who she loves and she will do anything to keep them safe. Oh, and she has the vibe of a mysterious person. And she hides some secrets. Thank you anyway!
If you know the drama Todome no Kiss, the main female protagonist is a little bit like her.
That sound exactly like Byun Ji Suk from Mask (2015). She is nice and clever, while the plot is basically about her trying to get money to live a better life and pay off the debts of her family so I guess you can see at the beginning of the drama especially that she would do anything for money (she even switches lives with a rich woman that looks like her). She takes care of her family and the male lead when they fall in love and their lives come as a priority to her (even the lives of her friends or people she doesn't know are more important to her) so she is a very nice and sympathetic person. Furthermore, she definitely has a mysterious vibe throughout and hides secrets from the other family she lives with, since she has to pretend to be a completely different person and hide her background.
I see you have already put Mask(2015) in your 'Plan to Watch' list so I will just recommend it as well, just to reassure you about your choice, since I believe you should really watch it.