Why would she be avoid me for no reason when i've only been nice to her?

Like she talks to every other guy expect me. But then will make small conversation with me when we're alone. She still said goodbye to me when she left last night. All I said on messenger was ask "how her holiday was?" But she read it but didn't reply. She and I have had conversations before but she seems to act like she doesn't like me. She has sat next to me or stood near me in the past.

Why would she be avoid me for no reason when i've only been nice to her?
Post Opinion