Just from playing a few decent Rain players I find that's a pretty bad match up, worse than 6-4 IMO. His pokes, his 4,3 kicks, into his amored roundhouse seems to beat armored grab for timing wise and gets a combo out of it or he can cancel it to screw with you. His wake up geyser makes it hard to do any follow up. Can't telestomp it and you don't really want to close the distance anyways, hes worse up close, can't grab at him, can't poke at him. Maybe its just the lag but even blocking and trying to air grab it doesn't seem to work. Also Sheeva's high damage combos are mostly all situational, Rain also has bigger damage combos that are more easily started. He can get a mid 40's combo off a 4,3 or a poke somtimes. Sheeva if she's lucky can get one off a low grab but you have to read it right and it can't be too far and it can't be in between pokes. It such a crappy gimmick.
Raiden is worse than 6-4 too I find, all you can do is poke at him to stop his 334's and b3, 1 2's , still doesn't even stop the f2, 4 really. At least if he teleports behind you I find a standing 4 into ground stomp can work but still you're not even getting 20% damage off that and if his connects he can get mid 30's or more. Most moves you'd try and follow up with after a successful poke he can teleport out of the way. It's a very frustrating match.
Cyrax on the other hand I don't find to be that bad. Cyrax who just try to set up nets and bombs full screen away, just block the nets, ground stomp when they toss a bomb and you can still move before the bomb can go off under you most times. If they teleport you can even d1 into an air grab while they are mid teleport. If they want to play rush down, you can armor through some things, or do some 212 combo set ups. If they are playing the full screen game a straight telestomp seems to beat out net if you both do them relatively at the same time from a decent read. I haven't fought any amazing Cyrax's in a while but I'd like to try it out a bit more.
But everyone has different play styles. So I may suck in some matches where others may do well and vise versa.
I do agree Kitana, Mileena, Kung Lao, Kabal, Cage and Reptile are all awful awful matches for her.