The last time you see her is when she helps the Parrs into Syndrome’s computers. You never find out what happens to her. So what do you guys think?
I think she probably went into hiding working at the NSA out of shame. Maybe Bob and Helen kept contact with her, you never know! 
Her future remains undisclosed (according to either Wikipedia or another book). But I see her turning over a new leaf and working for the SUpers or she could go into hiding.
I agree with what the others have said, Mirage going into hiding sounds very plausible. After all, she’s very good at disappearing. Either that or, as TSS said, her experience with the Incredibles might convince her to change sides and work for the Supers.
She probably went to work for some Russian super villain or maybe the NSA.
Appearently, in the boom comics, in the next issue, we see Mirage actually working for Rick Dicker/the NSA as an agent…
LOL That was great! I laughed out loud for that one.
All you guys have great ideas, but it’s amazing how much you find out from the BOOM! Comics huh TSS? 
Well, it’s just a preview from the upcoming issue for this week Konrad. I’m sure we’ll get more info when the comic is released.
While I’m glad that the comics have done so, I wish the movie would have finished up her story a little more. Perhaps when in the limo, there could have been a conversation like this:
RICK: We’ve frozen all of Syndrome’s assets. If he even sneezes, we’ll be there with a hankie and a pair of handcuffs.
BOB: You mean you’ve apprehended all of his accomplices?
RICK: Yes. Are there any that helped you out that you’d like to vouch for?
BOB: Well, there is one. Her name is Mirage. She gave us access to the rocket that got us here in time. Could you get her a reduced sentence or something?
RICK: I’ll see what I can do. I was looking through her file. She might make a good agent on our side.
BOB: Does all of this mean we’ll be coming out of hiding?
RICK: You just leave that to Politicians for now. You did good, Bob.
Heck, I would have liked to see Mirage working undercover at the track meet, perhaps making sure that Dash came in second.
In the comics, she went freelance, working as a spy for Rick Dicker.
Mrs Incredible still has Mirage issues though, as they spend a lot of the comic bickering with each other over minor problems.
My speculation is that once her employer was terminated (literally!), the Incredibles would have to take responsibility for the fact they just cost her a job, even if she was working for an evil mastermind.
I always imagined she’d be like Wade from Kim Possible, running a computer operations center from their new hideout.
Or possibly living with them, pretending to be a live-in nanny for her cover story (I’m assuming Mirage has to keep her identity secret too).
And that might be practical, since someone has to look after Jack while the rest of them are out saving the world.
I’m assuming she’d be more active if the team needs backup, given her combat skills.
And given that evil villians would want to try and kidnap a superbaby, it’d make sense to have a nanny who could double as a bodyguard.
Now picturing that scene:
Mr Incredible: Be nice to Aunty Mirage and don’t set her room on fire beat again.
It would also be funny to explore the conflict that MrsI has to live with someone she doesn’t like because they need her help.
Random thought, does Mirage actually have a real name?
I assume she has a birth name.
Although given her background in espionage, she would have made sure to destroy all physical records relating to her past and delete the digital ones from computers.