Couple things I noticed.
Random 6S is bad unless you have a HSB to cover your ass.
You are not instant blocking. This creates situations wehee you can punish, escape, and counter. example. millia jumps, throws pin, you instant block it, she airdashes at you, you 2K under her move because you can now do that from the instant block, you throw her.
You are not using spacing to bait her to come in at you in specific ways so you can counter em. Not only is the yo yo placement key for zoning so is your body placement. Out a HSS_6 out there and back way the fuck up. Millia will then try and get over your yo yo, leaving you options to counter after limiting her movement options. FD brake helps to keep the spacing at your control, always.
You should also understand: you two look very similar in skill and level. With some burst baiting, throws, Anti-airs etc. The speed characters are VERY HARD to trap. Especially in a casual setting with people you play with all the time. My point here: You will GENERALLY beat Millia more when you are at a higher skill level then her. Meaning you know all their options, you can predict what they are gonna do, and can efficiently maximize damage, bait, punish, and trap her.
There's lots more but this should work for now.