Everyone mourns a different way. There's no real right or wrong way to portray it.
As Major Tom said, everyone handles it differently. However, if the husband is dying over a period of time (no idea how long) then chances are she will have come to terms with it by the time he finally expires. She'd still be sad, but not a complete mess.
If I had to choose a specific way for a her to mourn, maybe have her isolate herself? She could lock herself up in her house or something, then emerge a day later, composed. Not sure if that will work with the story you have in mind or not.
Dreamkeepers Prelude, check it out!
Actually it's pretty sudden. She does break down at one point but her situation forces her to be a Woman Wearing The Queenly Mask and hide her mourning fom everyone else, but it's slowly revealed in situations where she's by herself
Then, that seems fine. That's how I pictured this as well, but of course, there's a good deal about this character that the rest of us don't know about.
"Jack, you have debauched my sloth."
So one of my female characters is married, but her husband dies over the course of the story. Obviously, she doesn't react very well to it (they had been married for about 15 years at least) she happens to be a bit of an Action Girl as well, so when I show her in such a vulnerable state, I don't her to become overly weak.