While she might have made a different decision if she knew the situation (for instance, maybe she doesn't want to be your girlfriend because she would want you to have the opportunity to have someone your age. A lot of people avoid dating younger people because they feel they would be taking something away from them. Learning you were married and poly could have made a difference) I would still go with leaving things be, at this stage.
She went out of her way to let you know she wasn't interested. I think insisting would easily be seen as disrespectful. You can probably still hang out at the club at least, and maybe more, but in a friendly way only. If the topic of your wife and/or your polyamory comes up, then sure, but don't force it.
I think that if you got the feeling that she wasn't interested, her exact phrasing might not matter. Sometimes people try to let you down nicely.
I am biased, because I have had a bad experience with "insisting". For instance, I asked a teacher out when I was in university, after the year ended. Because I was still going to attend the university (not with him as a teacher) he said, he couldn't date me.
I didn't think to say anything at the time. And if I had wanted to say anything at all, I should have done it right then. Instead, I went to him again later and pointed out that the problem was easy to solve as this university was hardly the only one I could attend, nor the closest to where I lived.
Long story short, while we had previously ended it on friendly term, he was really put-off by the fact I insisted and became upset with me, and seemed to feel worried by me (like I was some kind of stalker).
It was pretty hurtful, and I'm mentioning it here so that you know what my own experience is and how it is heavily influencing my advice. This instance wasn't the only time it happened (my insisting and ruining things), but it seemed to be the most relevant one to your situation.
If I could go back, I would still ask him out, because I think it's important to know even if the answer is no. But I wouldn't insist after being rejected, because I only made things worse.
I'm really sorry about how bad you feel. I understand you really like her. I hope you will be able to see her more and maintain a friendly relationship.