Keep in mind that you can move as slowly as you want. If you're not sure how you feel, make sure she knows that, and then take as much time as you need to figure it out.
It's not about whether or not to have a relationship with her. You already have that-- it's just been friendship for a long time, but it's a connection. You're thinking about adjusting that connection.
If you feel too uprooted by this, it is totally fine to say "maybe later." Take six months to focus on your friendship with her, and figure out your feelings.
If you previously felt content and now you *don't*, then listen to that. Give yourself permission to keep things the same as they have been.