Hi,
Chances of a TRV refusal are higher if it appears that the applicant has stronger ties to Canada (fiance/spouse) than to the Philippines.... and may, hence, overstay his/her visit.
Your fiancee must show very good reasons to return home such as her employment/family at home/property ownership, land or leased accommodation/good financial situation, previous travel history, etc.... with proofs.
Also, do go through the document checklist + Instruction Guide on the CIC website. You can submit additional documents to explain your situation.
To answer your questions:
Do I have to get her a plane ticket before I even apply?
No, it's not mandatory.
You can submit provisional flight bookings and mention that these will be confirmed when a TRV is granted.... or, if you still wish to buy tickets then do buy refundable tickets.
Does she also need to get a Canadian bank account or will her national one be ok?
Her local bank + bank statements for XX months for Philippine applicants.... no last-minute large deposits, nothing borrowed (do give an explanation for any large transactions).... and it must match her income.
Is it a good idea if I have a immigration lawyer handle the application ?
You can go through this forum to understand how to prepare a good TRV application. After that, you can decide whether you need the help of an immigration lawyer or not
Cheers