Grief affects people in different ways as I am sure you are aware. As you pointed out, that is at the core of your dilemma. It could be that she is fearful to get close to someone else right now for fear of losing them. That can be a powerful struggle especially for someone who has a tendency to internalize.

Personally, I would recommend being a resource to her. Try to think in terms of what you would need if you were in her situation. Being there for her as you have can mean a lot even if she hasn't expressed as much to you. Find ways to brighen her day with a joke or sharing an interesting anecdote or story. Occasionally remind her that you want to support her in whatever way you can and she is always welcome to turn to you for anything much like spondiferous suggested. Much of where things go depends on her at this point but you can be a source of stability and comfort available to her. Your loving patience is sure to earn you a level of endearment from her. When she is ready to move forward that could translate into her leaning in your direction.