Should I apply for a multiple entry visa if I may go to Tibet for a few days?

You may just apply for a single entry China visa. As for your trip to Tibet, you should apply for an aditional Tibet Entry Permit in fact. To app;ly for a China tourist visa in Malaysia, you may need the following documents:
1. Original passport remaining to be valid for at least six months from the date of application and with sufficient blank visa pages.
2. One completed Visa Application Form with a recently-taken passport photo stuck on it
3. round-trip air ticket
Your Australian daughter need to provide the original and a copy of her permanent residence or work permit which should be valid for at least 6 months in Malaysia additionally.
For the tibet entry permit, you should should contact the Tourism Administration of the Tibet Autonomous Region (Tel: 0086-891-6834313; Fax: 0086-891-6834632) and provide an Invitation Letter of Duly Authorized Unit issued by it.