My [22m] sister [7f] was adopted a year ago and we still haven't really bonded significantly/she doesn't particularly like me. Is there something I can do to help her feel safer around me?

She was adopted and at first she would barely speak to anyone. She was seen by pediatricians and the regular people from the adoption system and it wasn't a developmental delay, she was just adjusting and was understandably afraid.
I barely interacted with her in the first few months. I would try to talk to in low pressure environments while mom and/or dad were around, and she wouldn't really acknowledge my presence much and I kinda saw that she was a little intimated so I would back off.
Today she's very open with mom and dad and is adjusting well to school. I usually drop by their home once or twice a week plus the times when I drive either of them around and she tags along. I say hi and she says hi back but doesn't interact with me further than that. If I ask stuff like how's school she gets visibly uncomfortable and doesn't say anything. Sometimes mom or dad give me the answer for the question and she stays quiet.
If mom and dad say things like "hey your brother's here" she'll wave at me but won't interact further than that and sometimes even sort of hide behind them or cling to them if I approach her.
Last weekend dad and I were repairing a water pipe, mom was doing the laundry and she was at the kitchen table drawing. I asked her if she wanted chocolate milk without really expecting an answer, just sort of letting her know, and she jumped and said "yes!". I got her a small ladder so she could reach the counter and she whipped the milk while I prepared the rest. I asked her a few things and she was very receptive and we probably had a more organic interaction than any other in the past year. Mom was really happy to see us get along.
So, that was really fun and I wish we could have more of those. I drove her and mom somewhere yesterday and it was more like all the other non-interactions we've had before.
I like her a lot. I love that she's part of our family and I feel a strong impulse to take care of her and make sure she's OK, and I wish I could be closer to her. I see her having a good time and being perfectly comfortable being around our parents, telling them stuff about her day, cuddling them in the couch, little things that, and I wish we could share them.
I understand that it is all up to her, she's still adjusting, and I won't ever pretend to cross any boundaries into uncomfortable territory for her. As general advice, are there things I can do that would contribute to making her feel safer in general? To adjust? And ways bond like last weekend?
Edit: Thanks to everyone for taking the time to make thoughtful suggestions. it means a lot and there is very good advice I'll try to use the best possible way I can.
tl;dr: Little sister was adopted a year ago, she's still adjusting and she's extremely shy around me and we mostly don't interact. Is there anything I can to help her adjust and ways for us to bond?


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