It depends on what the trust specifies about your ownership and whether it gives you any options about selling it.
As a practical matter, you are not very likely to find a buyer for half the house if your sister is hostile to that idea.
And no, you cannot force your sister to purchase your half unless the trust specifically provides some way for that to happen.
If you think that your sister is actually squandering trust funds by spending them on the house, or on herself, in a way that the trust prohibits, you should seek the advice of an estate planning attorney.
All states have rules about what accounting information a trustee is required to provide to the beneficiaries, and, if your sister is spending the money improperly, she will have to pay the trust back. If she refuses to cooperate, it might be time to ask a court to intervene to require that cooperation or replace her as a trustee.