Help with romantic question..Old friend I cant tell if she is being nice or flirting!?

We dated a year ago and then broke up.We have been talking the last few months and last night I called her and we talked for about a half hour.I needed to say more so I texted her with ........"When I think about you I get very (devil emoticon)" any way she texted back with a "winky face" and have a good night! Is she interested or just being nice!??Please help