She knows you are poly?
But you haven't expressed interest?
I say, let her know you are interested in taking her out on a date, if she's up to it and see what she says.
Don't press for relationship changes.
Just open the door.
I have a friend who lost her husband. It's been almost 2 years. She's very heavily involved in widow groups. But she's also in a new relationship.
The reality is-that she lost a key piece of her life and it is traumatic. that won't go away, it's just that you learn to live with it. But part of that is learning that it's ok to miss them and talk about them etc-for the rest of your life.
Open the door. Don't push.
"Love As Thou Wilt"