If the attraction is becoming an issue and interfering with your progress, it's probably a good idea. On the other hand, if it's not, I don't think it's something you should feel like you have to tell her. I would just prepare yourself for any and all possible responses so you aren't blindsided. I think she will be kind though and will tell you there is nothing wrong with your feelings, although nothing can happen between you (which you know anyway). I think you'll be fine and if you feel strongly you should tell her, but just go with the flow and don't pressure yourself.