grammaticality - "Decided to do X the next time she went for a walk" vs. "...the next time she goes for a walk"

I came across this sentence in the book Grammar Essentials for Dummies which confused me.

The lion with a thorn in her paw decided to wear sneakers the next time she went for a walk in the jungle.

Why is it went instead of goes? I always thought the next time indicated something in the future.

Answer

In terms of time, it's not necessarily in the future.

It's in the future-of-the-past. The event of the lion next going for a walk is an event that can take place any time between the past event of her making that decision, and what is still the future. It could be tomorrow, but if the lion decided this last week, then that walk could have been yesterday.

Since the superordinate clause is in the past tense, backshifting can bring the subordinate into the past too.

On the other hand, if we we had that clause in the present tense:

The lion with a thorn in her paw decided to wear sneakers the next time she goes for a walk in the jungle.

That suggests that this walk is asserted to still in the future. Backshifting isn't required for a statement about the present or future that still holds.