Hi Rebecca and thanks for this question about Willow.
I'm sorry to hear she is not showing affection and understand that this can be upsetting.
Unfortunately, for some cats, being sociable and affectionate is just not in their nature. This can be a mix of genetics and life experience. With her, she had a really tough start in life, and this is likely affecting her relationship with people now.
Cats have a critical socialisation period between from 2 to 7 weeks when their interactions with humans shape the way they seem them forever. If they have negative interactions, they are primed to not trust humans when older.
Though we won't ever be able to change her personality, often with time, trust will come. The more she trusts us, the more she might come out of her shell and choose to spend more time in our company.
It can help to offer 'low pressure' game and play options. So, we can e.g. play with a laser or wind up toy near her, and she can join in if she wants.
We can also set up things like food puzzles and scent trails, to keep her engaged.
If anxious, it helps to use calming products to settle nerves. This can include a Feliway plugin and daily calming supplements.
It is important she has some hiding spaces within the home where there is no foot traffic, so she can get some time to herself if needed.
We msut never force interactions, hold her on us or hug her. These sort of things make cats distressed when they're not on board, and can undo the other hard work you're doing. Any close contact like this must be on her terms.
The hope is that, over time and as her confidence grows, she may show some affection. Unfortunately though, not all cats will do this in the end.