Just because you are capable of having multiple orgasms with one partner doesn't mean you owe more sex with your other partner after you orgasm once.

Now that she knows her body is capable of more, there's no reason she should reserve that for one partner only

The reason is that she doesn't want to, that she said no. It's really simple.

Not when it would make her life and all of her relationships better.

If by make her life better you mean validating her partner's irrational insecurities and entitlement to her body, then sure. Why are you so insistent that it's okay to pressure someone into doing something sexual that they don't want to just because they are capable of having multiple orgasms?