actually, her English doesn't sound American...it sounds more Aussie...
Hmmm, sorry dear to disagree.
She definitely does not sound Aussie. Our Aussie accent is a bit harsher sounding and we do not roll our "r"s, etc. Maybe she sounded Aussie to some because her voice and intonation sounds a bit nasal. And some Aussies especially the ones in the outback are kinda nasal in their intonations. Lol!
Other than that .... definitely Thai-cum-American accented English. But hey, nothing wrong with that yeah. Her English is understandable and relatively good.
I guess I am a bit bias too as my partner is Thai. At work, he sounded so Aussie and you would have no idea where he came from. But when amongst his Asian friends, he kinda like a chameleon reverted to his Thai-cum-Aussie accented English. Which to a certain extent I find kinda cute.
Still on the subject of accent, I love the fact that when I meet people, I try to guess their origin through their accent.

Not really hard at all I say ... and kinda fun too.