I had just played in a hand against this person. She didn't bet with a set of 5s on a board of AK5 and only bet 75 cents on the river. When should I have folded this?

PokerStars No-Limit Hold'em, $0.25 BB (8 handed) converter

SB ($36.60)
Hero ($25)
UTG ($46.60)
UTG+1 ($12.45)
MP1 ($9.50)
MP2 ($3.75)
CO ($55.15)
Button ($28.10)

Preflop: Hero is BB with T, T.
4 folds, CO calls $0.25, 1 fold, SB completes, Hero raises to $1, CO calls $0.75, SB calls $0.75.

Flop: ($3) 7, 2, 8 (3 players)
SB checks, Hero bets $2.5, CO raises to $5, SB folds, Hero raises to $10, CO raises to $54.15, Hero calls $14 (All-In).

Turn: ($81.15) 3 (2 players, 1 all-in)

River: ($81.15) 6 (2 players, 1 all-in)

Final Pot: $81.15
Main Pot: $51, between Hero and CO.
Pot 2: $30.15, returned to CO.