Yeah in general he can outspeed her with aGA and b6. 6B and 3A also usually do more damage per hit than her long range options. I just don't like getting into a distance game with him because honestly Ivy's dmg in CL is pretty pathetic and I don't like risking a stepped 6A+B and get punished by Sieg 1B or worse. It's hard to encourage Sieg to come close to you, and once you finally get close to him, he can get out of range with pushback moves, 4B+K, etc. Sieg is pretty difficult to deal with once he opens up to more than 3B, aGA, and throws.
Pay attention to the first round of this fight:
Siegfried's damage is just alot scarier than Ivy's CL state damage. And the only quick WP poke that stands a chance against b6 is 3A, and that move only gets you so far.
My fights with Offbeat are actually a little different than this, I am surprised he was being so aggressive against Malek. He usually turtles me alot more because he already knows about everything I've said. I rarely even get a good opportunity to use SW mixups, because Sieg has the ability to 4B+K most of your moveset even if you have advantage. The A+B from stance is pretty impossible to punish as well. Not to mention he can 2_8B+K almost everything except WP 3A, WP WS A, etc after getting something blocked at tip range(even NH 1K!). He will then go in SCH A/SCH A cancel, delays, mixups, etc. He has the ability to keep attacking you if he catches you at mid/long range and you aren't in WP. If you try something like CL 66A, well you just have to weigh a 66A hit vs. his 6B (which TCs), and his 3B.
Sieg can be a bitch.
/endrant
Anyway the fights that give me trouble are :
Hilde
Amy
Sophitia
Siegfried (actually only OffbeatNinja)