Gee, I am a new aunt. Where is my "aunt shower?" I could use some new things and I never turn down money.
You are right, this is extremely poor etiquette. If your co-workers want to do something special for the boss, they should take her out to eat on their own dime. They should not be pressuring you to buy a gift or donate money to a collection for the boss, who probably makes more money than you do.
In their desire to kiss up to the boss, your co-workers may have committed another social blunder. Since I am guessing that everyone knows who is responsible for this, I suspect there may be growing resentment toward these individuals. If they continue on the trend of ignoring the real life important events of their co-workers while hosting parties for their boss, the boss may figure out their motives and she may be unimpressed.