Contact Form 7 can be made auto responsive in a Divi site by simply adding in the appropriate CSS code to allow it to happen.

Add the following to Custom CSS

/* Contact Form7 mobile styling */
@media screen and (max-width: 768px){
.wpcf7 #Personal-Details, .wpcf7 #Education, .wpcf7 #Profession, .wpcf7 #To-Teach, .wpcf7 #Timings, .wpcf7 #Colscol, .wpcf7 #Upload {
height:auto;
padding: 20px;
}
#Teacher-column #left {
width: 100%;
float: none;
margin-bottom: 20px;
}

.input-text, input[type=email], input[type=password], input[type=search], input[type=tel], input[type=text], input[type=url], textarea {
width: 100%;
}

span.wpcf7-list-item {
display: block;
margin: 20px 0 0 1em;
}

.wpcf7 #Upload p{
line-height:21px;
}
}