Right now - be angry, it's ok to be angry, you uprooted your life to rush to support her. Likely you would have if she was honest, but she didn't give you the chance to decide how to feel about it. let that simmer for a bit, and then TELL her how you feel. Tell her she needs to hear you out so you can have some closure with your feelings. If she can't hear you out, then look for a therapist so you can share your honest feelings and get some feedback and still get that closure even if it's not from an apology from her.

Long term - you and your family needs to set your sister up with the services she needs so she can live her life without your support. You can't just keep throwing money at her. She needs to figure out how to qualify for any daycare subsidy, single parent government supports or rent rebates, food banks, even long term financial support for things like recreation activities for this child. Find housing that can support her eventual salary (maybe she moves home, or rents a small apartment?) How can she get some training to upgrade her skills to upgrade her employment opportunities. She can either be a victim to her circumstances, or she can be a champion and make choices to move forward and above.