Low Flush v. Loose Button

BTN was 71/17/0 after 24 hands; early on, so no real reads other than loose over small sample. we'd taken a couple of standard pots off of each other previously

PokerStars No-Limit Hold'em, $0.02 BB (6 handed) - PokerStars Converter Tool from FlopTurnRiver.com

Hero (BB) ($5)
UTG ($2.07)
MP ($1.77)
CO ($1.20)
Button ($4.05)
SB ($2)

Preflop: Hero is BB with 9, 7
3 folds, Button calls $0.02, 1 fold, Hero checks

Flop: ($0.05) J, K, 7 (2 players)
Hero bets $0.03, Button calls $0.03

Turn: ($0.11) Q (2 players)
Hero bets $0.07, Button calls $0.07

River: ($0.25) 9 (2 players)
Hero bets $0.15, Button raises to $3.93 (All-In), Hero ???