My girlfriend has a blister on both of her feet on the toe next to the big one and they developed red streaks?

Infection? The problem may have started as a hammertoe rubbing on the inside of the toe. However, the red streaking is a real concern and probably is a sign of an infection that has to be treated.
See a doctor. Red streaks coming from a souce of infection such as a blister, sore, ulcer or other break or breakdown of the skin could be serious. Streaking usually means bacteria have invaded the blister and are now going up the lymphatic system. You may notice enlarged lymph nodes in the groin. I believe you should be seen right away. Antibiotic will probably be necessary. Don't delay.