Even IF she can get a SETV, the visa does not gaurantee her entry to Thailand. It's up to the immigration officer on entry, and depends on his/her mood, previous foreigner stays in Thailand etc...
How long is a piece of string?! Have your 3 proofs but no one can say you won't be pulled up, questioned or declined entry, even having a tourist visa is no gaurantee. Someone else's experience may be completely different from your own, it all depends on the individual traveler history, IO and their mood of the day.
I know the Thai Embassy in Canberra accepts expected travel itineraries, don’t need actual bookings, best bet is to check with the consulate directly as to what they will accept.
You do know you can’t stay 6 months without leaving Thailand, max 60 days + 30 days extension on each entry before enter before date expires!
your multi entry doe NOT start when you first enter...its starts on the date the Visa was granted, and finishes 12 months from the grant date )not entry date)...so if you leave and return ANY time after 12 month of the grant of the visa, then you require at entry permit to use any existing permitted to stay previously provided.
Things are harder now - tourist visas, Visa Exempt, Visa On Arrival etc and ED Visas are no longer viable options for regular travel or lengthy stays in Thailand.
Your only viable options are as Tod suggested, otherwise you risk denial of entry based on history of previous stays.