I'm sure she looks like she is smiling. Her mouth is open wide enough to make it seem like it. I observed animation to know that it will seem like that. Personally I think the suicide cut scene makes a little sense considering she manipulated her own son,Kovu,almost completely ignored Nuka,tried to kill someone constantly,I think she would have done suicide. just saying.

When they were making the movie, they made an alternate scene when Kiara offers herself to help, but then Zira says: "No... never!" and releases her claws, commiting suicide. They thought this was going to be too dark for a kid's movie and removed it.

I don't think she commited suicide, personaly I think she was smiling because she was remembering how scar had met her. Maybe that was the same river or something.

That editing was most likely don quickly and in last minute, so yeah, there are a lot of leftovers. Like smile and camera thing. It was probably too late to make new scene, so they did what they could.

Officially Zira did not do suicide. She just refused help from Kiara, due to her hate and stuff. And then she fell... It also is not shown if she actually died, again because movie is for children too, but generally it is believed that she did. I can't really imagine her surviving that fall and river with fast current which was also full of logs.

that cyut scene of Zira commiting suicide was creepy
i do think she commited suicide so she could join Scar,
im not really sure if she really died o not though...

Well if you seen the movie the camera looks away from zira then when we see her again she is falling so yes I think she commited suicide

Yeah, they forgot to remove that smile. So it is leftover from original idea.

Well, that was the orignal idea, until they decided "Hey, its a kids movie, she can't commit suicide!" So that's why she is smiling, but she really just falls.

Watch this:
http://www.youtube.com/watch?v=HoctlRyGdf8