I understand your concerns, I agree with the other posts, an X-pen seems to be your best option. Try not to get too upset with the in-laws, they're used to living their lives a certain way and don't have all the worries that come with having a small dog and it sounds like they don't have the same concerns with their existing dogs so it's not surprising that they forget "the rules" when you come over. I think it's wonderful that they allow you to bring her, you're very lucky
I think bringing an x-pen will make for a much more relaxing visit in the future
.