Is my coworker flirting with me ?

I am new to the office. I have been employed in the last 5 months. When I first started working she used to act nervous around me. She smiles and look down when we make eye contact. We barely talk but I saw her looking at me couple of times. I didn't read too much into it. Recently I noticed that she is more comfortable around me. I lift and I am fit so they usually ask me to carry heavy stuff in the office so this time a team member asked me if I could help him then I can hear in the background she was saying "yes you need muscular man". The other day I was carrying something heavy to my desk and then she said to me " ohhh muscles". Was she flirting?
Is my coworker flirting with me ?
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