If she insists so much for a D.L., it must be that the department or certain individuals were starting to 'gossip' or pass not so pleasant comments about you or your work. She took the initiative, and went far and beyond her call of duty, maybe because she knows you are a far better person than the paper trail delay. Your co-worker is a STAR. I would get a vard, and write a heartfelt thankyou note, and perhaps mention that words aren't just good enough, you would really like to do something special whether for her or her family.
Tell her you won't take NO for an answer, and promise you'll keep it on a D.L. as well.