I experimented with vegainsm and vegetarianism throughout the years, and giving up milk and soy isn’t too tough. The real key is to eat whole, nonprocessed foods. They add soy in processing of a lot of thngs, that’s true, but not to whole foods. For four months, it wouldn’t be too bad, and knowing there’s an end should help!
The real problem with not doing so, is that if she actually has a sensitivity later on, you’ll have to feed her those foods, and you won’t be familiar with it.