Use a better palette because red is trash tier.
Your nair spacing is probably the biggest thing you need to work on. Almost every time you naired his shield, he was able to grab/punish you. Nair has pretty decent range, so you can pull back near the end of the move and still hit with it.
I can remember if you got any grabs, but uthrow>utilt (at low percents) or uair (at higher percents, but it's not guaranteed) is your friend.
If you want to get fancy, you could try incorporating Lunar Landing into your gameplay. LL fair is quite easy to do and combos into uair until nearly 100%. LL bair is cool for covering your back. LL nair and dair have only 1 frame where you can do it without getting the landing lag, but they're both pretty useful. LL nair is probably the best one and you can do stuff like LL nair>roll behind them so they get hit with Luma's first kick>usmash (since Luma drags them into it). Dair is one of Luma's best kill moves, so being able to safely throw it out is really useful. LL is also very useful for covering landings (which is something Rosalinda tends to struggle with since she's so floaty).
All in all, gj sisT.