My girlfriend got butt injections a year ago, and now one cheek is hard. What do I do?

This is a very unfortunate story i hear from at least one patient per week in my office. Best your girlfriend seeks a consultation with a board certified buttock implant specialist to assess the current situation and be prepared for any reconstruction in the future. Often the hardening and skin discoloration worsens over time and eventually may require surgical removal.  Glad to help. 

You have done the right thing by contacting a doctor. Ensure you get in ASAP for the appointment that way if it is anything that needs serious medical attention it is not delayed. 

I'm skeptical that your girlfriend's original procedure was even legal.  "Someone named Michael who comes from FL to Houston" to do these procedures...??  That's not a situation I would trust.  It seems that your girlfriend is now having a complication due to this procedure and should see a board-certified plastic surgeon for consultation and treatment.