This is probably the right answer. It's still weird in my head because it's effectively absorbing the cash into my budget and then deciding to take it back out of a budget months later. I do think there's some responsibility on the part of the gift giver to understand how their gift impacts the recipient. It's why pets are almost always a bad gift. I also get tripped up putting myself in her head because I don't grasp why she thinks cash is a great gift. It was when I was 15 or 20, but at 38 when she's 71, it isn't. It feels kind of infantilizing.
I hear ya... but you are still 15 in her head. Especially now that she's 71, and her perceptions of the world are narrowing down, new memories are harder to store/recall, and she spends a lot of time in her old memories. The gift isn't about you; it's about her. Accepting it generously is going to make her happy. And that's just a nice thing to do for another human being, regardless of your relationship with them.