She could have sent it to many colleagues, it's always good for people to not burn bridges, and have social networks in the work setting.
If she sent it to other people as well, that's probably what it is. Find out.
If she sent it only to you, try to exchange some texts (ask her how she's doing), and see the tone of the text. If there are a lot of emojis and exclamation marks, and the general tone is flirtatious, then take it to the next level. Ask her out for dinner and see what the response is. From there, it should be easy to see if she's into you.