F4 Red Dash option select is great. This is useful at max distance, about sweep, for the f4. If the f4 whiffs, since you've already input the Red Dash command of df3, the f43 string will just come out. If the f4 hits or is blocked the Red Dash comes out and if its blocked you can slide, or if it hits you can down slash for all of that damage.
Red dash then Slide is good in the neutral game if you are at the perfect range because the dash covers a lot of space and a slide from max distance is 0 on block and still safe on block otherwise, however a lot of characters knock her out of the dash animation before the slide comes out so I think its important for Skarlet to mix up Red Dash then immediate slide vs. delaying the slide. A lot of people that I play just block low all day cause they can fuzzy any non enhanced overheads, so what works great is to show them you like to slide, show them a delayed slide, let them thinking blocking low means they are safe, that opens up throw attempts after Red Dashes, and blockstring pressure after empty Red Dashes. Again, she is wide open to get hit during the dash but it is a good footsies tool. Sometimes a cover dagger before a dash is nice, an instant air dagger then dash is nice, or even a ground dagger canceled and then dash in is nice too. The daggers are used to lock em down, that gives you room to dash in.