If the wedding is being held some distance from where you live, then the invitation to livestream was probably an attempt to be considerate. ...And, no, you are not required to send a gift. (A sweet e-card congratulating the couple would be a nice gesture.)
Unless you want to foot the bill for your SIL on this trip (to which she has invited herself), you'll have to summon up the courage to tell her you will under no circumstances be doing that.
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