We have Dtwins (5). The gap of expectations of the 2 of them are getting wide enough now that dd is noticing and we're just not handling it well. DD is NT, DS has severe behaviour issues, deaf, rare gastric problems. Recently we've had CAMHS involvment with DS's behaviour and we are doing what they say to the letter. So only working on 1 behaviour with rewards and all others are ignored or if very bad then time out. So at the moment he gets a sticker in his cars pixar sticker book if he can play with dd for 10 mins without hitting her. If he manages it then LOTS of praise, big fuss and a sticker etc. But the ignoring other minor things (like eating with fingers instead of cutlery, chewing his toys etc) is causing a problem with dd. Her behaviour has really deterioated. She's copying him in most things now and then says, for example "if I can eat my dinner with my cutlery can I have a sticker?". Well, no you can't you've been doing that for years. She does get stickers in her book for not arguing with me/dh and not picking her nose! So its not like she doesn't get a chance to get stickers.
Then over our one week holiday we were doing scrap books. Our expectations for ds was just to draw a picture every day of something that he liked. For dd our expectation was to draw a picture and write a sentance. This was easy for dd but just to get ds put pen to paper is a challenge. So it gets to the point that dd won't write because ds doesn't have to. DD can read WELL above her age, ds can't read at all. DD now won't read because ds doesn't do it. There are a number of examples, I could go on and on, you get the gist I hope.
She doesn't see that he's different, just see's him as naughty. We can't very well turn round and say that she has to do stuff because she's older or whatever. How do others deal with this?