How can I tell if a co-worker likes me?

Ok. So every time I go to work and we see each other she always smiles real big, and always seems excited too see me, she says things like yay! you're here, or I called in running late but made it on time and she was like Sweet you made it on time and she set up for a high five. Shes always making small talk but mostly asking how im doing which might not mean anything, but the other co workers she smiles at also, she doesn't smile as big and as long as she smiles at me. She always seems really excited to see me and is very friendly, but she doesn't act like that with other co workers, could this mean she just knows im friendly and thinks im cool or what. One more thing, she told me she thought I looked disgruntled one day, and wanted to know if I am sarcastic or serious. I plainly said I tend to be sarcastic, she then smiled and said good me too. And she said if there is ANYTHING i needed to talk to her about, I should come to her, Again she might just be friendly and doing her job.