Hello. I would love to design a room for my mom for her 50th birthday. She loves USA and Red, White, and Blue. Although our house is nice my parents room really needs some updating. It looks like a disaster from the 1960's (with lime green carpet and flowered bedding & curtains). I was thinking of getting blue carpet, keeping the white walls, and doing a deep red bedspread and curtains. She is conservative so I thought this could be a suttle way of using the USA theme. Any suggestions.

Don't do a blue carpet, please!! Do a cream/tan carpeting, like a berber-solid color though or a loop/pile carpet-good for wear. That way, if you decide to change themes, or she doesn't like the theme, you are not stuck w/ blue carpeting-you'd only move up a decade w/ that color carpeting.
I'd make the theme more subtle, with decorations. There are plenty of Americana decorations out there, just try not to go over board w/ nicknacks. You could do a white bedspread in a chenille-all the rage again. Find a flag square decorative pillow for the bed. Or maybe a red/white and blue quilt or use the quilt as a throw.
Careful w/ red bedding and curtains-it may end up looking a bit like brothel.
The paint doesn't have to be stark white-a cream white would be nice-I have dover white from sherwin williams-you may have to ask for it by name. Or even a neutral creamy-tan would look really nice w/ red/white and blue accents.
If you google Americana decor, there are plenty of websites to choose from.
good luck