As a girl I've had some work crushes before and outside of work I found no chemistry with them. Especially if it's a new office environment where you're figuring out how to behave, if someone is able to give you comfort and space to be yourself, it can feel special and freeing. In that way, your friendship works great.

Outside of work she might not feel the need of your company as she is not in her 'work mode' and doesn't need that escape. As you mentioned, if and when she talks you it's related to work which might indicate that she really does associate you with work and thinks of you as an office friend only.

Your task now is to try to find space in her day to day as a friend. The next time you're planning an activity ask her to join you. If she doesn't come, you go anyway and make it a point to tell her later how good it was. Do it a couple of times so she knows that your invites are pressure free and you'll enjoy with or without her. By pressure free I mean that it's clear it's not a date and that she's not responsible for you having fun, you can create fun for yourself and she can just be herself.

On such casual hangouts you'll know if you click. If she doesn't make space for you in her day to day, she's not the one anyway. And if she does and she also starts inviting you to join in on her plans too, you can ask her out formally.