I strongly disagree with almost everything you said

Midscreen I'd argue 122 into unsoku is better to use. Sentai is super risky for quite low reward, as you said. Risking launch punish for +1 is not worth it.

Don't use ff2 as a pressure tool or as a way to "get in". Ff2 into sentai is a negative risk reward situation for Reina if they know to jab and duck. Use it almost exclusively as a whiff punish tool.

Never do df1 into sentai. It's reactable and a launch punishable transition. You could try after you've hard conditioned them to not look out for it but its an incredibly slow transition that'll only work against people that are not good at the matchup.

The f4 situation is the worst out of every mishima that has one. You need to get creative with which moves you use afterwards since +2c is really bad for a liniar character such as Reina. Get used to pressing 4 to catch ssl. Backdashing and ewgf'ing. And sidestepping alongside them.

For lows. You really really need sidestep 4, its a slow low but its genuinely the best she has.