If you fully lose the fight and choose Retry as opposed to Retry during the fight, the match eventually becomes easier after around 10 losses. You'll get health between the opponents and they get hit more. I think it gets even easier from there too.
Regardless, with Mileena your approach should be to save your bar for XRay, and mixup the fight with a couple strategies:
1) crossover jumping punch into uppercut while she's walking toward you
2) If she's a bit father away, sweep her multiple times until she falls and keep sweeping. You can also use this if she blocks one of your aggressive attempts. Then move back to tip 1
3) Don't try to throw her because she often gets priority
4) If tip 1 is failing, keep your finger next to block if she's far, hold onto it when she's close and wait for her to botch rolls and teleport kicks. You have to wait a split second to throw your spear after the roll because when she bounces off you she goes above the spear. If you wait a split second you can catch her
5) Teleport into a combo. Use this sparingly as you can get severely punished
6) XRay when she starts a move once you get it, even if you get hurt your Xray will connect
The AI is smart at this level so you can't abuse just one technique or you'll get punished, but I found that once the difficulty drops, if you mixup the techniques she'll randomly fall for them. Your bread and butter is jumping punch into uppercut, punishing her specials with Spear combos, sweeping Xray, and random teleports.
If you have enough health when you reach Shao, it's just a matter of creating distance, and waiting until he does a move, and following up with a teleport/spear combo. If he's close do the jumping punch, uppercut combo.
This fight was much easier than 251 to be honest.