I see nothing wrong with respectfully letting her know but making it clear that you're just sharing your feelings and you don't expect her to reciprocate. Let her know that you aren't going to bring it up again, and because you value your friendship, you don't want anything to change unless she wants it, but that if she's ever feeling up to it, you would be interested in pursuing a relationship.
Sure, it's possible it might remind her of her loss, but it's not like she isn't thinking about it every day anyway. I can't imagine how just telling her you're interested could cause her any harm, as long as you don't pressure her or keep bringing it up.
Indeed, being reminded that she's still a lovable person might be just what she needs to take the next step in the healing process. Who knows? Everyone is different.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker