Perfects are statives, not eventives, so there is no inherent ordering; quite the contrary, the “default” implicature^∗ is that the events are simultaneous or overlap.

However, the implicature can be overrideen (for instance, through adverbs like then); and by and large hearers/readers will understand the sentence to communicate what you call the “logical” order.

More to the point, perhaps, is the fact that the second perfect is not required, or even particularly desirable, once you have established the anteriority of the email. I would write it this way:

The meeting took place because he had sent her an email, which she then forwarded to other members.

^∗ a useful technical term I've just discovered and have been looking for an excuse to share. It means something implied but not entailed. That is, it is a likely but not a necessary consequence of the context: you may infer it, but the inference can be ‘cancelled’

Perfects are statives, not eventives, so there is no inherent ordering; quite the contrary, the “default” implicature^∗ is that the events are simultaneous or overlap.

However, the implicature can be overridden (for instance, through adverbs like then); and by and large hearers/readers will understand the sentence to communicate what you call the “logical” order.

More to the point, perhaps, is the fact that the second perfect is not required, or even particularly desirable, once you have established the anteriority of the email. I would write it this way:

The meeting took place because he had sent her an email, which she then forwarded to other members.

^∗ a useful technical term I've just discovered and have been looking for an excuse to share. It means something implied but not entailed. That is, it is a likely but not a necessary consequence of the context: you may infer it, but the inference can be ‘cancelled’