No. "Release letters" are not an American "thing". We are free to leave any employer any time we choose, for any reason, or no reason at all.
Your problem is your prospective employer getting a labor certification, proving that there are no Americans who can do your job. That is unlikely since you work in IT.- Lisa A
The date the visa expires is not important. Your I-94 should say D/S which stands for Duration of Studies. As long as you are enrolled in school and in good status you are okay.
File for Change of Status for her the same day you get the I-20. Personally, I don't think you can get it done in time for Fall Semester.- Yak Rider