I'm afraid to tell her how i feel

Well, I would advise you to make sure first that the girl is still single. If no, then I guess you just have to find another one or wait for your chance but waiting in vain is not a good idea. If the girl is still single, then you have to tell her how you feel for her. Well, don't just suddenly pop in front of her and tell her immediately. You have to get to know the girl first. Start by making short conversations with her. If you do this often, you'll eventually proceed to the next level and deepen your relationship with her. This way, you can also assess if what you're feeling is real love and not just mere physical attraction. Being afraid of rejection is the dumbest thing to do. If you really like her, you have to tell whatever her response may be.

Instead of worrying if she'll reject you or not, why not talk to her first? Try to strike up small conversations. The next time you meet her, try approaching her and say "Hello" or something. Introduce yourself and tell her that from the other division. Also mention that you kept seeing her when you're in her division so you decided to approach her. There's nothing wrong with that. Small conversations like "What's your work here" or "I hope work's not that tiring" is a good way to start small conversations. I think it's a bit too early to worry on how you should tell her how you feel since you don't even know the person. Telling her that you like her without even knowing her first is kinda.. Well.. Creepy :P Try to befriend her first then from there, you can slowly find out if she's single or not or whatever. Don't worry about rejection first. It's too early for that :D Think of some way to close the gap and know her first. You can do it! We'll be rooting for you :D