I think that if Maekawa was only afraid of being alone, she could have hitted on any men in the office (seems like they like her already).
But instead of doing it, she took her chance to approach Shimizu when she found out about the yuri event. It's also clear that she had some kind of interest in Shimizu since she started working there.
Not only that, but she's really mean towards Shimizu, I don't think she would do that if she was only using her for company. I believe what she feels for Shimizu is so strong that she can't put up her facade, being honest of who she really is for the first time in a long period.
She may not be in love with Shimizu yet, but she really treasures her.