I don't know what country you live in, but I don't think you should be too paranoid when it comes to the amount you plan to donate. If it was millions of dollars, then maybe someone would invest resources in trying to identify the donor, but in this case, the investigation would cost much more than the donation.

Of course, you will increase your privacy even more if you break the link between your BTC and the mixer you choose, but you can never expect it to be 100% complete privacy. Such things simply do not exist when you are online.