If her college is really shutting then the priority must be to find another college and legally change her visa conditions or she will be forced to leave UK.
Without a valid visa she will become illegal.
Without a valid visa she cannot legally work
Without a valid visa she cannot file for divorce
Without a valid divorce she cannot legally get married
No offence intended, just trying to focus you (and your gf) on the short term priority.
On the issues you raise about marriage be careful about motives. Try to look beyond the passions of the moment. To me there is already a red-flag.
If you believe in your heart that you have found someone you can grow with, and you have enough faith to be convinced that you will not regret the road not taken and the partner not chosen then you may be ready for marriage.
If not, then wait.
Study the way she cares for others and the way she deals with the daily affairs of life. If that makes you love her more then your love will have a good chance to grow.
If it doesn't, tread carefully.
If you can't respect the way you each deal with the world around you, eventually you will not respect each other.
A well made marriage is worth the patience in waiting for it.
