As it is known, it has long been noticed that fates of twins are often closely connected or similar, and that many twins, even when they were separated since birth, can have the same habits, get into similar situations, have the same diseases and even die at the same time. However, this rule does not always work. The reason is that if twins were born within one 24-hour period (and sometimes it is not the case), then they as if share the natural (subtype) program, and one gets the active part of the program, and the other—passive.
Since active and passive of the program of each one of 293 subtypes of Homo sapiens are recorded by completely different images, which give different personality traits, abilities, life algorithms, preferences, etc.—twins might differ from each other in all these parameters.
Unfortunately, if this is the case with the situation that you described, then you cannot see these sisters separately—as active and passive—from the decryption of the program of your girlfriend. Probably you would recognize one of them in the description of the active part of the program, and the other one—in the description of the passive. However, any decryption is a certain “fusion,” where the active and passive of the program are tied together. Therefore, the only way to see the passive and the active (separately) is to find out images of this subtype program. However, it is never too late to get images of the program of your girlfriend.
A second possible reason that twins might differ in character is that the time of their birth was at the junction of two 24-hour periods. In this case, programs of different subtypes turn on in each one of them at the moment of cutting of the umbilical cord. For example, assuming that birthing occurred normally, and in this case usually the time between birth of first and second twin is 20-30 minutes—the first twin was born at 11:45 PM, and the second at 12:15 AM. This is also a possibility, especially since in many cases birthing of twins occurs with complications and the process of birthing of the second child might be delayed.
Therefore, if you state that your girlfriend and her twin sister are not alike at all—they either each got one half of the subtype program, or if they were born at the junction of two 24-hour periods—they have different subtype programs. It is difficult to say which case applies in your situation since you have not provided time of birth of each of the sisters.