I am knitting a scarf with relatively thin yarn (which uses 4mm needles). It has got pattern that is to be shown by the knits and purls. But since the scarf rolls along both edges which makes it difficult to wear… I’m thinking felting it but is worried that the pattern won’t be able to show after felting… Does anyone have any idea whether the pattern will be “flattened” after felting??
~Yoyo
I suppose it depends on how much you felt it, but in general I wouldn’t recommend felting a project where you want to be able to see the knit and purl stitches. If you end up felting it, the pattern created by the knit and purl stitches will be obscured and you might be disappointed since you put all that hard work into creating a nice pattern!
To avoid issues with the edges rolling in the future, you might consider creating a border around the edge using a stitch that does not curl … for example, garter stitch or seed stitch (among others) can form a nice border for your work. 
It depends on the type of yarn whether it will felt. You may be able to do a light felting and have it work, but I’m not sure.
The pattern will disappear with any but a very light felting and the roll will get worse, in my experience. You do need a border on it to keep it straight. I’d crochet one that compliments the pattern.
If you are thinking of felting it that woudl imply you are knitting with a feltable fiber (wool or alpaca) so why not just block it?
I don’t know what pattern she’s using (other than that it is a knit/purl pattern), but I assume that at least portions of the scarf are stockinette … blocking won’t completely eliminate the curl effect of stockinette, especially after it’s been used for a while.
If you really don’t want to add a border you could try blocking it and see how well it works, but I’m sure you’ll still have some degree of curling. I think the border is probably the best solution. 