Hmm, I felt sympathetic up until the point where you mention the things the woman says she has bought.
I mean, hmm, okay, sometimes you can have different "envelopes" of money for different things (like keeping your money separate for groceries, fun, clothing, and stuff) but I'm sorry, when one envelope, like groceries or bills, is empty, well, you just empty the others. See what I mean ?
For example, I'm not in such a nice financial condition myself. People could have had that thought about me. But why am I in this situation, you might ask ? I used my store's credit card and maxed it (I work for the store) and, while maxing it, I bought all of the Sims 2 games existings (minus Pets) , I bought myself an mp3 player, stuff like that... I would totally understand that someone wanting to help me would be pissed off by this, even though no one should judge what I spend.
There's a friend, for example, I lent 300 euros to. She's been in a dire financial situation lately but has done some things (went for a haircut, bought DVDs, little "trinkets" like that) during the year (been almost a year since I lent the money) that could have amounted to the money she owes me. Then I figured, hmm, she needs to take the stress off, after all these troubles... plus now she has a baby boy, so she needs all the rest she can get. Sure, I might be leaning on the "You're not going to see your money again" side, but as of now, I'm just thinking she deserves to be enjoying herself a little.
The woman in the OP, on the other hand ? Total crass. Here they are, all the coworkers, thinking she's suffering such financial hardship that she can't let her children have a decent Christmas... and poof, next thing they know, same coworkers hear her bragging about new expensive stuff.
I wouldn't give a dime and would tell the others "chipping in" coworkers why.