Q: Can women perk up their breasts by working their pectorals?

A: I don't think the effect would be noticeable for the vast majority of women. Men can achieve significant muscle growth, including in the chest area, which can significantly alter the look of their chests. Most women, however, would not be able to achieve enough pec development for that.

If a woman loses significant amount of fat (through weight training or otherwise), her breasts will typically get smaller which may give more of the effect you're looking for as compared to working pectorals to raise the chest.