Some bleed heavily for weeks, some just spot here and there and some have 'silent' seasons where you see no colour at all, or are so clean you just don't notice they have cleaned themselves up. To be on the safe side keep her away from males for at least three weeks or even longer (I had one got at by her son on day 30 after he had been in kennels for two weeks!). Even if there is little colour they are normally quite swollen, and with a Boxer it is easy to see as they don't have any long hair to hide their bits.