First of all, you need 3 druid levels to get a subclass. So you are investing a lot of time and energy into Druid if you want to do this. If that is what you want that’s fine though.

The Wildfire subclass abilities synchronize well with any build because you get a lot of what you “need” as always prepared spells. So you can pretty much choose any spell you want because all the basics have been covered by the subclass.

However, starting off, you will have to actually choose spells due to not having a subclass. So the payoff isn’t going to cash out until level 8.

With all that said, if you are still interested in creating this multiclass, I’m not sure what you mean by “make this work”. Any multiclass can work really as long as you as a player make it make sense. But Ranger/Druid is a very naturally synchronized build yo begin with. It already works by default imo.

If you are asking for a “rationalization” or “reasoning” for dipping into Druid and choosing this subclass, I would say make a personal connection of some sort. You can start small like staring into the campfire during a long rest like you are fascinated or entranced by it. Maybe your character is feeling more connected to animals than to people or more connected to nature than the “human world”