OP thinking about this a bit more, I think it would be unfair of you to focus on what you do for her parents and aunts or on the way you hoped she might want to help your DD.
And I think it would be a big mistake to say so to SIL or anyone else. You will come across as resentful and it might upset your DH, PILs and aunts as well as your SIL if they end up thinking you don't actually want to do the things you do for them.
You say you are happy to help anyone who needs it, as this was the way you were raised.
But in bringing in what you do for other people of your own free will, and suggesting that SIL should remember this now, makes it sound as if you are not actually all that happy about helping those people out.
Are you helping them because you really want to help them?
Or do you see yourself as only doing what SIL should be doing if she lived closer?
It's hard to say without knowing what it is you do for them, or how capable they are of managing without you.
But really if you help them it should be because you want to, which you say it is, or to help out your DH as they are his family/responsibility just as much as they are your SIL's and he is the one you are married to.
I know you say you were brought up to help and that this is about reciprocation, but unless you really do believe you are only fulfilling your SILs responsibilities, the people most obliged to reciprocate to you are the PILs, aunts and your DH. They are are the ones most directly benefitting from whatever it is you do.
And where you say "Thirty minutes to help someone who has helped her parents a fair bit seemed a reasonable ask", I think you have to remember that you actually didn't ask, reasonably or otherwise, until after you had won the clarinet.
And at that point, she really couldn't say no.
Is it possible that the three telephone calls checking arrangements and asking her to chose a time and date to collect it have left her feeling a bit pushed to hurry up? Rather than making her think she could collect it at her convenience, she feels she has to collect quickly because you and your DH keep calling her about it?
For someone who normally takes a while to reply to telephone calls and emails, three calls to ask her about the arrangements and if things are okay for her could feel quite pushy.