Valerie Gameplan:
She wants to use B,B (hold forward during those to get more range) to threaten to poke for 2 damage, or at least do 2 levels of block damage if they block. After that she can either do C (safe, and gives you a full chunk of block damage on block) or B (can crossup).
Valerie also wants to do air B and air super any time she can get away with it. Air B is a crossup that’s good vs people who are getting up from a knockdown, and if it hits, then B,B combos for a total 3 damage. Air super can completely wreck them you catch them in it and then do stuff like air B once or twice if they block, or B,B,B.
If Valerie is far, she can use air C to get in. If it hits an airborne opponent, they get knocked down which lets her do air B or air super as they get up. She can also use ground C to get in sometimes, and the startup of it goes through fireballs.
Beating Valerie:
You already heard about keeping her away or using invulnerable moves. The OTHER main way to win is rush her down so hard that she can’t do anything. That’s what Setsuki does. For example, Setsuki air C, cancel to divekick, land and neutral A kick, then C starlight tumbler. At this point, Setsuki can either finish with the C tumbler throw or go for a divekick. If she divekicks at the earliest moment, it beats anything Valerie would do (including jump!) other than ground super. It’s an oppressive lockdown and puts you in control as Setsuki. Get Valerie to be afraid, then use the C throw option, and that leads to a reset where she’s stuck in all this again. This forces her to ground super, but you can try to bait it / get her to waste it. And even if you get hit by it, you have several seconds where you can rush down Valerie again without worrying about her super.