Goodness, how ridiculous. This healthy food thing at school has gotten way out of hand, in my opinion. A treat should be just that, a treat. And that means sugar (should I put that is the "bad word" category and put an asterick in it when I type?? :) )- as they don't get cookies and cupcakes at home much. I think that if you keep something from kids, they just want it more. When they are older, they will rebel and eat a cookie or candy all they want when you are not there. Then, they won't know how to eat it in moderation and get fat. You teach them to make proper choices and have good physical activity. The school parties and birthday parties are fun and should not have restrictions on them in my opinion.
I would consult your school parent handbook on their food policy. Our public school this year has gone on the no sugar bandwagon as well. So, I am stuck following their rules of no sugar laden things. I posted a thread on mamasource on preschool healthy treats about a month back and got some good ideas. I am going to make a fun fruit pizza. With cream cheese and I am going to make a Halloween type picture out of the fruit. I think the kids will like this- I think your kids would like it too- who doesn't like pizza??. I saw some fun, healthy ideas on:
http://familyfun.go.com/recipes/special/specialfeature/ha...
As far as how to deal with this mom, I don't know. I am not big into confrontation. I would just tell her that you are following the school parent handbook on treats and tell her what you are making. Then, change the subject to some other detail on the party- decorations, games, etc. Stand firm and don't let her push you over on your snack idea. If she wants toothbrushes (ok?????), then she can handle asking parents for that part. You should just make sure that you handle the sugar side, and she can handle the healthy side. Combine the two, and give the kids choices. Kids love to pick what they want, and both sides of the debate are happy. That is my opinion. Good luck!