While Thelma's holding up the convenience store, Louise remains moping in the car, sore over having lost all her cash to a hot cowboy. She looks morosely out of the Thunderbird and makes eye contact with some weird old lady who's staring right at her. Is that her? she wonders. (Not actually, but we think so.) Sometimes, when you see an old person, you wonder what your future will be like. Will you be old and alone with a creepy pink dress on, too?
It's likely that seeing this old woman makes Louise double down on her quest for freedom.