When she first got her record deal, she signed an exploitative contract. Which is a pretty common thing that happens to newly signed artists.
Whether her family should have been in the position to get her a better contract or not, my opinion is the same.
It's true that it's completely legal for the new owners of her old record label to own all her old recordings ...but I honestly can't fault Taylor Swift for publicly complaining about scummy behavior that goes on in the record industry, even if it's legal for them to do, and even if the complaining is self serving for her own benefit.
Basically my opinion is if you own someone else's music, expect that they will complain about that fact and just live with it. Treat it as an expected cost of doing business and move on with your life as the new owner of their music. Getting into a feud via the press with the artist doesn't do anything for me.
And I say this as someone who was NEVER really a fan of Taylor Swift, and I think there are other much better pop artists.