I'm a mileena player myself, and it's just came to my mind. i quess after every string you can do a sais, it makes it more safe, and than you can do something else? try it out?
You don't want to be cancelling into sai's all the time especially as strings like 23 and 11 lead to juggles with roll. Cancelling into sai's is good for moves like f3 1+2 though which are unsafe and 234 for extra chip, you can also cancel into ex tele kick then sai's for block strings too.
How exactly are people pressuring you? Is it just normal strings or are people cancelling them out etc? Mileena's can apply great pressure herself and she has one of the best d4's in the game with Sonya which you should spam the shit out of until your opponent does anything to counter it. Her U4 gives advantage on block and online you can mix it up wth b3 if the lag is strong enough lol. Some block strings give advantage on block or have no or little disadvantage which is probably why your having trouble online. Unless you know the strings ultra safe then running up to them and trying to pressure isn't always the best option a good idea is to jump and cross them over when blocking things too.
If your getting uppercutted often then its likely your running up to them and then going for a high string which uppercut happy players will catch. Her 23 (I think) should mainly be used for punishing and you'll likely get most of your juggles of her normal ball roll and air trades into ball.
Once you condition your opponent and they stop rushing you down mindlessly then that'll open up more opportunites for you to put on the pressure. Use d4 and do half strings then throw etc, so long as its not online and against 24 low hat I think Mileena can get out of and apply pressure fairly well.
