If she's doing CC dsmash, bait it out or don't do things easily CCed (or shoot lasers, lol). Dair can beat it at 0 (don't do it too high), shine can beat it, dtilt and bair can beat it after some percent. If you have the opportunity to grab her, you can do that too. If she doesn't try to move after CC, you can do other things provided you're fading back or well spaced, and punish dsmash with whatever you want.
If she's attempting FC aerial dsmash/whatever mixups, hit her if she's not starting a fair, not floating back, and close enough to hit from an immediate short hop out of dash forward when you're making you're decision (but you don't have to use an aerial). If she is starting a fair roll or wavedash in the direction that would put you farthest (or far enough from to not get hit and give you the best position) from where she'd land if she would start falling right then or is currently falling, or simply dashdance punish, or laser her out. If she isn't in range or is moving back, just wait and try to get the best position you can or punish something dumb she does. If you try to challenge her air to air, just slightly above max SH laser height means you can uair, lower means fair, a little lower means nair.
If she's dsmashing on platforms or something, don't approach from below. SH uair may be able to safely poke her from certain heights, and you may be able to crouch under certain lower platforms on FoD. Feel free to experiment with this.
Basically, try to not get into the situations where you're being dsmashed.