I am so happy for you. Super-sleuthing does pay off! 
Well, first off, if they were willing to give you the number, then heck sweetie, go for it. It's not like you got the number off the black market. 
Guess the woman thought you were an honest soul and trusted you. Gee I am sitting here in anticipation, can't wait to hear where this takes you! I'm sure she will be delighted to hear from you. She will also respect the fact that you were apprehensive about doing so though. It shows respect for she and her family.
Bottom line, whatever you are comfortable with.
Ah, told you Michael was a great man. I just heard from him yesterday myself. I really admire him. Top notch in my book!
Three cheers to you for aggressively going ahead with your research. 
Proud Daughter of Walter (Monday) Poniedzialek
540th Engineer Combat Regiment, 2833rd Bn, H&S Co, 4th Platoon
There's "No Bridge Too Far"