Good kashrus makes good neighbors
I know this particular question was time sensitive, but hopefully I didn't get to it too late to be of some help.
I became good friends with a woman who moved into my neighborhood here in Israel. Her husband told me that even though they are not observant, they keep kosher so that everyone can eat there. She mentioned that on Passover she keeps her hametz in the refrigerator. I explained to her, as neutrally as possible, that hametz that wasn't sold couldn't be eaten after Passover, and she said she would take care of it. She never mentioned it again. Even if she sold her hametz, which I presume she did, I don't feel comfortable eating there. I imagine there is a lot of halacha that she doesn't know, and I don't want to quiz her about sifting flour or trumot and maaserot. She is hosting a meeting on Monday and most of the women keep kosher. Because I know her best, the other women will be looking at me to see whether I am eating the food, and I know that my friend is planning to cook and bake. Please help me explain tactfully that her food might not get eaten!!!!
-Not The Kosher Police
You are in a sticky situation and I really don't envy you. It does sound like you are a person with tact and you will need it! You were direct with your friend about the chametz situation and she seems to have responded well to it. The Monday meeting is going to be a tricky situation, in Israel even eating a piece of fruit can be a complicated issue and there will be no way to fake your way out of it. The bad news is that if you are going to be a true friend to this woman you are going to have to talk to her about all of these things.
Remember, she is doing her best and this is not personal.
Let her know that you care about her and you respect her but that keeping kosher is VERY complicated and you don't want her to be hurt when people turn down her Shabbos invitation or pass up her homemade cookies. Offer to learn with her to study the halachot and where they came from. It may be a bit tough at first but it may prove to be an enjoyable activity for both of you.
For now I would encourage her to BUY the food she serves at the meeting until the two of you can figure out how to get her kashrus status up to a level your neighborhood will accept, and please let me know how it turns out - I'm rooting for you!