You can try to space Ayane out too though you're reducing the match down to a battle of patience (which kinda favours Smart Ayanes). Mila's ranged game revolves around her good pokes (4K, 4H+K or 2H+K are nice), crushing something with 3H+K or attempting to gain Frame advantage (or Keepout) with 66P or 66K. But I'll let you know that 6T is your friend against Ayane.
Just relax! That's it literally. Ayane's typically come in two extremes. Either extreme turtling or extreme aggressiveness. Personally I mimic whatever style they choose and let them fuck up as they always do trying to play one or the other extremes. There aren't any lows to worry about either so composure is key. Your faster and hit much harder.
Lol, If the Ayane player is playing aggressive they're either in their opponent's head badly or are likely playing her wrong. But yeah, letting the Ayane player fuck up is the key to beating like, 90+% of Ayane players. She is not easy to use and most people don't know what the hell they're doing with her. Ayane can dig her own grave easier than anyone (except Phase 4).
And for the record, saying Ayane has no lows to worry about is false information. Aggressive/rushdown Ayane is a terrible way of using the character since you're blatantly ignoring her tools. Most utilize spacing are bad at it. Also, Force of Nature is on the money about Ayane being bs online, scrub play and flowchart is dumb due to latency.