She might be nervous about what you're saying or doing. If your friend has been avoiding eye contact with you for no apparent reason, then it could be because she's feeling uncomfortable around you. Maybe she feels like something is off or awkward between the two of you and doesn't know how to address it properly yet. It's best to give her some time to adjust before bringing it up with her again later on in the conversation or another time when things are less awkward between the two of you — then maybe she'll be more willing to talk about whatever it is that has been bothering her lately.