Visiting my Mom moving to work in Shanghai

My mother is moving to work in Shaoxing (next to Shanghai) in little over a week. I wanted to go visit her from around the 22nd of December which should give me at least a month time to prepare.

At the time of buying my return plane tickets to Phnom Penh from London, I didn't yet know about my mom moving to China. I found out that I am able to change my plane ticket with my airline for a fee of $100.

My worry is that it's complicated, because I heard that I need to buy tickets to and from China before even applying for a visa, but it feels risky because if it doesn't work out, I would have to pay a total of $200 for changing my plane tickets twice. Another worry is the fact that my mother doesn't have all of her Chinese papers yet in case I would have to provide them when applying for a visiting-a-relative visa.

So what do you suggest I do? Also, should I apply for a tourist or a visit-a-relative type? If I book an appointment for 3 days later in Phnom Penh, would I be able to take care of everything needed for the visa in that one day?

Thank you