Yes the Rose match up is hard for Ken, I have trouble with her too. Rose was the first reason why I decided to get more theoretical about SSF4. Learning frame data and stuff. I was having too much trouble with her slide and spiral so I decided to improve my knowledge about the game. The thing you said is true TeeJay, if she spaces it well, she is safe, and maybe have some advantage if the spiral or her slide is made correctly. You really have to watch carefully during the fight her spacing. If she spaces it right she can counter you with frame traps, EX spiral, or do a safe BD. Even if you do a kara HP SRK I think she can escapes with BD after a safe blocked spiral. Not sure. But if you see her doing the spiral wrong or maybe drop her BNB with ex spiral, very common with beginners, you can punish at least with c.MK or maybe c.HP.
Those well spaced moves and her pokes are the things that make this match so hard for Ken. Her s.MK is an amazing move against shotos, she avoids c.MK with a fast and unthrowable move. Very useful. Good Roses pokes a lot, pushing Ken far, and are always on point with c.HP for anti air. The way Ken should win this match is very similar to Guile’s, you should get a knockdown and mix her up with no mistakes. Punish her BDs with c.HK OS, and do safe jumps on her to get her reversals stuffed. In comparison to Guile I think she doesnt control space so perfect as Guile, Ken has more opportunities to get in, since her fireball is not useful as Guile’s. Other thing very important people forget about is her throw range, it seems like she has a automatic kara thow, very very good range for a normal throw.
Other important thing, I recomend that you look at her patterns during a offensive string. Good Roses know that a string finished with spiral or fireball is not safe, can be SRKed, specially by Ken, so its very important to watch how she is finishing her strings. If you anticipate a spiral or a fireball with a fierce SRK, she will be more honest during her string and respect you more.
Finally, dont do too much fireballs, she can fill her meter with her reflect tools, dont abuse of air tatsu, can be stuffed by her c.HP, try to do your best to get damage and knockdowns mainly while she doesnt have meter cause her wake up is very limited, she has an amazing BD but it can be OSed with c.HK, be careful when she has full bars, she can make an easy big damage/comeback with that, throw her a lot, and do your best to push her to the corner.
Peace