R.K.
Try to make a deal with her. Ask her to go to the school where she is already signed up for at least a semester hopefully you can convince her a year. If she still wants to transfer to be with the boyfriend then she can.
My daughter was talked out of college and into marriage at 19, filed for a divorce at 23. She is now 29 mother of 2 step-mom to 4, married a second time and trying to finish a degree. She got her Associate's but wants her Bachelor's maybe a Master's Degree. Her second husband is great and very supportive.
It was impossible to convince her at the young age of 19 that the boyfriend did not have her best interests in mind. He wanted to get married and convinced her he had money set aside for her college and he would be supportive ... uumm didn't happen until she left him.
I tried and her older siblings tried to tell her to wait a year but she refused.
Remember she is an adult and can run off and marry this guy anytime she chooses. So be careful how you word things and keep telling her you only want what is best for her. NEVER say anything bad about this guy it will only make her cling tighter to him.