One thing about Shampoo to keep in mind: Ranma HAS to marry her eventually. No ifs, no buts, sooner or later they have to marry, for two reasons:
The engagement to her is the only one LEGALLY BINDING. Ranma defeated her in her village and by their laws they're engaged, and the laws of Chinese villages are absolute (that's why Panthyose Taro NEEDS Happosai to change his name, his village law say that his name is up to the person that first washed him after he was born, and since that happens to be Happosai in a rare moment of being a decent person he's stuck with something Happosai thinks is a good name). If Ranma tries to marry anyone else, Shampoo can sue, and while that's a legal quagmire the only other fiancee that can afford a good lawyer is Kodachi, and that's without the diplomatic fallout from a Japanese citizen being engaged to a Chinese one by his own volition (initially by technicality, by his own idiotic actions after the Reversal Jewel debacle) and then marrying someone else.
If Ranma goes and marries someone else anyway, Shampoo WILL kill them. Not a guess, this was SHOWN ON PAGE in the manga when the engagement got transferred to Nabiki: while Nabiki was able to get Ukyo and Kodachi to try and buy the Tendo engagement at an auction, Shampoo arrived and tried to kill her instead.
I dare say that the reason Ranma and Shampoo aren't married already is only out of her kindness, as she could press the situation any moment.
