Re: venting... this is long...
I am so sorry for your sadness and frustration. This forum is here for you.Whenever you need to vent or just cry, this group is here. I wish I could give you a hug, it is soooo very hard to watch a friend suffer. You are greiving and need to talk about your feelings, I know your husband has suffered a loss, this makes it harder but talk with him as well, find a support network or a group for cancer families-they include friends.
As far as co-workers and residents at the LTC, as a friend and supervisor you can share info about your friend, ask her what to tell them. I am sure just saying she is very sick and you are unsure when she will be back would acceptable, and a cheery note from staff would surely be good for your friend, if she doesn't want visitors, you could take care packages from the LTC to her, think of the smiles and inside jokes you could share going thru some of them. You may not get to go crafting or out to lunch, but you can spend time with her, she needs you.
Hang in there, but give yourself permission to cry and be angry for your friend and for yourself.