I've seen a mix throughout my career. Some company cultures are very forward/cc heavy (some are very bcc heavy... ugh), others seem to want to treat everything as one on one conversation.
Personally, I prefer forwading or looping people into conversations as opposed to maintaining a series of parallel conversations. Unless I've never ever seen anyone do it, someone tries to correct me, or someone gets upset, I'm going to forward/cc.
In this case, I would Forward to Jared Gray. (Forward because Susan clearly doesn't want to be on the thread)
(I'm going with Susan being the person you originally reached out to)
I'm having XYZ issue and Susan indicated you are the go to for this. Any assistance you could provide would be appreciated.
Two positives to this approach: You won't get a situation where Susan sends you to Tim who sends you to back Susan, and Tim now has the full email chain where you described your problem and potentially did some back and forth with Susan before she decided it was Jared's domain.
If I were in Susan's position, I would have included Jared on a Reply All with something like:
Tim is having XYZ issue which is part of that thing you're responsible for. Can you please answer his questions.
I would likely end up staying on the exchange during a series of reply all's, but it doesn't really bother me to dismiss future emails, and I'm a naturally curious person who would be interested in the answer, even if I never expect to need to know.
There are of course times when you should not loop someone into a conversation, but those are generally few and far between. Unless you're in a management/leadership position or working some super secret project, your email communication at work generally shouldn't include information that would be inadvisable to forward. Just use your best judgement if you think that might be the case.