A question of etiquette.

At the theater tonight, the woman sitting behind me gnawed her gum loudly throughout the entire play. This was not a rollicking, toe-tapping musical; this was an extremely serious, dramatic study of a family dissolving into abuse and alcoholism. And she was smacking away, open-mouthed, like a cow chewing her cud. It was disgusting as well as distracting.

What's the proper etiquette? Should I have turned around to her early in the first act and asked her to chew more quietly? Should I have complained during the intermission to the house-manager (who would most likely have shrugged and said there was nothing he could do)? Should I have done my best to ignore her?

I ended up not saying anything. Initially I had hoped she would finish quickly and after I realized she wouldn't, it felt too late to say anything. So, I suffered in silence and seethed.