By the law of Shit happens yes I would in a heartbeat.
Say she's the 6th best 1500 runner in the word going into the season. By factors of others getting injured, busted for doping, having off days, her improving her odds at winning are way greater than 1 in 100.
If you ask what is the most likely scenarion then yes I'd likely lose my $1000. But I think the odds are heavily enough in my favor that would be a good bet.
1500's in championship races do have some unpredicatbility and people you don't think would win can, see Centro and Simpson in recent years. Hell Manzano got a silver and he was a much bigger shock than Muir would be.