Does mathematical modeling expert need to know subject of interdisciplinary field
Yes, absolutely - up to a point.

You do not need to be the world's greatest expert on the subject matter, but you will need to know enough to participate in the research process and make suggestions. If your role as an applied mathematician is "Subject matter expert gives you equations to solve, you apply numerical method," that is consulting, not modeling or research. Here are some things where more subject matter knowledge improves the life of both applied mathematicians and their collaborators:

With more chemistry knowledge you can know


What approximations could be appropriate? What information do your collaborators really need?
Do the results you have make sense? Being able to determine simple checks and analytic test cases yourself will save a lot of time.
If you can answer this question, what is the likely next question?
If the suggestion your collaborators gave you has a typo - this is obvious with more subject knowledge, but can be missed.
When you report on your work (papers, talks) - you can be specific about why it is important


I have worked in many math/[other science] collaborations, and a very common failure mode is that a math student takes a couple of weeks, and comes back with a single result, with an error that could have been caught. Or that the student mis-interprets a suggestion, and it takes a long time to clear up. Or that the student spends a month optimizing a calculation that is only relevant to an order of magnitude.  All of this happens a lot, and the best solution is more subject knowledge!

I do not know if this is happening with you. But if you are modeling a chemistry process, you will either need to learn a good amount of the chemistry, or you will need a more well-defined problem at the beginning. And as a modeler, you presumably know that defining the problem well is half of the battle!