I believe you have every right to require that your SIL either prepare, or allow you to bring, sufficient GF food so that your husband and daughter not only have enough to eat safely, but feel as if they too are welcome members of the family whose well-being, comfort, and happiness are important. And considering the lack of knowledge and consideration she has displayed about this in the past, I think you are much safer bringing the food yourself, or skipping dinner.
I simply cannot accept any excuses from a close relative who refuses to take simple steps to safeguard the health of a family member in these circumstances. And yes, I do know what is involved -- our family does it all the time. We have one with celiac, vegetarians, diabetics, people who are lactose intolerant, and one with a raging shrimp allergy who will eat the shrimp anyway if we put it on the holiday table. We have kids who like plain food, adults who are dying for the somewhat fancy foods we only make at the holidays, and men who just want meat. And everyone has a favorite dessert.
We manage to keep those with health issues safe (the vegetarians have been meatless for so long that they would get really ill if we snuck meat in any of the meatless dishes), and to make everyone happy without going crazy. Yes, I know the preferences aren't as important as the health issues, but it all works out.
A holiday meal is special because it is a time to express our love and caring for each other. Somehow saying that "she can find something to eat, I suppose", or whatever the SIL's version is, just doesn't cut it.
Go ahead and make a fuss.