Why is my sister so attached to her new friend?

My sister is 33 and she just met this woman that is kinda ...wild . LOL. Well since she met her she has been dressing better, wearing makeup. But the thing that catches my attention is my sister never likes to use up gas and stuff and drive any more than like 10 miles. For anyone. She has been going to this woman's apartment 33 miles ONE WAY about 3 times a week. hmmmm