Me and my girlfiriend had sex on 22 dec 2015 but I entered half of my penis wearing condoms.. but she is not still having periods as her periods date is 6jan 2015.. is she pregnant or what makes her periods delayed?

Periods can be delayed for many reasons other than pregnancy. Her period is only 4 days late, that can happen from time to time. If she doesn't get her period in the next few days she can take a pregnancy test using first morning urine.

You did have sex, 1/2 way, just a little or all the way, there is a chance. Wearing a condom is great, and it does provide a lot of protection, but condoms do have a high failure rate, so there is a chance of pregnancy. No birth control method is 100 percent, so any insertion of the penis may cause a pregnancy.

A few days late is often common, cycles do not come exact all the time, the stress and worry over pregnancy itself may cause them to be late, as in changes in diet, and other factors.

So now she waits and if her cycle does not come in a week, she should do a pregnancy test, using the first urine of the morning, as soon as she wakes up