Nemonemsis
If you really want the answer to your question, as regards your sister, might I (kindly) suggest you do the (I suspect) painful work of really burrowing down into the (I suspect, quite challenging) thoughts you block with the phrase, 'It's her choice'?
Seriously, hiding behind there will be nuances of your sister's negotiation of the paths available to live as a woman in a gendered society; a history both individual and social, of how she has come to understand and experience pleasure, joy, boredom, exhilaration in contemporary society; economic imperatives ... and also your responses to those (which will be complex).
Again: that's not exhaustive.
You could spend years in therapy working through it with an attentive listener.
The point is: it's not simple.
As a society, we seem to have an absolute mania for stopping thinking. And we do it through the deployment of this phrase, 'it's her choice'.
It's bizarre, because it goes hand in hand with a dominant discourse telling us we have never had more freedom about our emotions, never had more choice.
It's the strangest thing.
What are we - as a culture - so frightened of, that we (as a culture) insist on locking so much away behind this door charmed shut and barred with this 'magic' phrase?
What monsters are we too frightened to face up to?