With the updates, I think the most important thing is for DD to clear her name before resigning. I'm not sure I agree with PPs mentioning the receipt, because all this woman has to do is say she can't find it or she threw it away. Heck, that's even believable. Then it's back to square one.
If the other committee member can't or won't get involved, then I think DD should send an email, but without mentioning the receipt. Just tell her she's seen these around, she knows exactly what they go for, and there's about a $120 deficit to be returned. It would be great if she could get the other person to be part of this email, and a few bcc's sent.
The bcc's may be a little dodgy, but when someone else's actions put her reputation at risk, she needs to fight back. Etiquette doesn't say it's ok to be a doormat.