It's not like I'm short on pearls, since I cleared the event dailies and also had some left from yesterday. So I put 100 on Yulan and 30 on each of the other girls.

Admittedly, I could've spread out my bets differently to make a specific win regardles of who'd win, like:
10 on Yulan (*100, payout: 1,000)
20 on Priscilla (*50, payout: 1,000)
33 on Hollyhock (*30, payout: 990)
50 on Southern Cross (*20, payout 1,000)
100 on Aster (*10, payout 1,000)

Total cost would be 213 pearls, where I invested 220 pearls now.
But, 1,000 cocktails isn't too much compared to what I gather on a day, so I think spreading out the investment more evenly would yield better winnings.
Placing 40 pearls on each girl would yield:
Yulan: 4,000
Priscilla: 2,000
Hollyhock: 1,200
Southern Cross: 800
Aster: 400

Betting 100 pearls on the top 2 girls for each race would probably be more profitable in the long run than betting any pearls at all on the last two girls.