Sometimes with donations at a DC, CA, and SA the WT will tell the members how much the costs of the hire of the venue was and then give out the attendance figures. They will then say "we will leave that with you brothers". Many work out how much it costs per head and contribute that much. This is deceptive as the venue has already been paid for by surplus funds.
Sometime donations are solicited through different means by articles and talks at the KH. Members are encouraged to donate to a variety of projects, usually if a member cannot participate in some building project they are guilted into donating funds as a means to doing God's will and salvation. It's all about the money it's all deceptive.
Personally I agree with mynameislame, as to the controlling of funds. This will push her to being more deceptive. If this is not disposable income, lay your cards on the table and show her where the money needs to go. If it is disposable income then really it's not fair that she is assigning it to charity without discussing the use of funds with you.
Perhaps you could sit down with her and spend the money together, doing something you enjoy as a family, maybe dining out in fancy restuarants that she can get dressed up for. But appeal to her Christian nature and say it's not fair for her to assign the money with out discussion regardless whether its charitable or not.
Kate xx