Yes, I would recommend that you include evidence (in her application, of course) for your work contract + a leave approval letter from your employer + any critical work commitments that you must return to after the intended visit + your bank statements (to confirm salary transfers), etc
Is it possible for her to register for the conference before she applies for a TRV?
When do you intend to visit? Hopefully, you are not applying too much in advance
Do include the car ownership documents + repayment statement.
Also, do include any other evidence:
Rent agreement, 2-3 recent rent receipts, highlight the bank transactions on the bank statement + if her family is financially dependent on her + any personal/family commitments that she must return to after her visit (evidence is required)
Do include evidence of enrollment + tuition fee receipt + exam fee receipt and exam schedule, etc.
If this is an online program, it won't really help much as a tie to return to.
Does she have credit cards (even if her bank balance is more than adequate to cover the visit)?
Just 3-4 pictures would suffice + your marriage certificate
From your sister + copy of her passport + her financials (if she would like to provide those, it is not mandatory for the host to give these documents)
You can mention you don't intend to apply for spousal PR just yet. Do be careful about how you word this from a long-term perspective keeping in mind her PR application later.
You can also include a small explanation/evidence on the monetary/career benefits that you are hoping to achieve by staying in China for the next two years + something similar for her career
It does not matter