Mariah Carey's Assistant Brushes Her Hair After Going on Rollercoaster Ride

Mariah Carey always has someone around to make sure she's looking beautiful -- proven in these pictures ... which show the rule applies even when she's hitting a theme park.

The singer was at Universal Studios' Islands of Adventure in Orlando Wednesday -- where she was celebrating her twins Moroccan and Monroe's 13th birthday ... and Mama Bear herself ended up getting on one of the rides, which sent her 'do into a frenzy.

The photos are pretty freakin' hilarious -- you can see MC hanging on for dear life as she gets whipped around on the rollercoaster ... and her long, luscious locks are flying high.

No harm, no foul of course -- but Mariah wasn't about to start walking around the park afterward and let her hair look like a damn mess ... 'cause she had her assistant start brushing her mane as soon as they were back at ground zero and steady again after.

Mariah was totally into it too, flashing a big smile and waving to paps who were firing away.

We'll give credit where credit is due ... Mariah was clearly game to get on the ride and enjoy the good time with her kids -- but hey, she's an icon too ... and needs to maintain her gorgeous appearance. An icon's gotta do what an icon's gotta do ... eye-rollers be damned.

As for the festivities ... it looks like Mariah and her ex, Nick Cannon, have been celebrating the twins' birthdays for at least a couple of days now -- and clearly, they go all out for them.

Based on what Mariah's wearing in these pics -- a customized birthday shirt for Moroccan and Monroe -- you can tell they got all the love in the world for their children.

You can call her a diva if you want, but at least she knows she's fabulous. Get 'em, Mimi!