I agree with the other posts. Give it more time. Research the links on introducing cats. There are many posted throughout the forum, and timskitties has posted some that are exceptional. You can also just "google" 'introduce cat' as well.
It is normal for an existing cat to be upset when a newcomer is brought in. Don't take it personally. She will get used to the kitten, and it is possible that they will form a tight bond over time and enjoy each other.
Just make sure you give your 1st kitty lots of love and affection, and maybe slip her an extra treat or two from time-to-time. It takes patience and a bit of effort (not to mention emotion) when you add a family member. We have added cats to our household, and were always met with some hostility toward us or the new kitty or just a "cold shoulder". It will get better as she gets used to the new baby.
Something you can try: (I haven't done it myself) is to rub the kitten with a dry and clean towel then rub it on the established kitty and back again on the new kitty. I may not clearly understand this, but have read that when the "smell" of one cat is put on the other cat, it will make them less likely to reject each other. Please verify this with another member who knows more about it, or who has done it, ideally. I just scanned it in one of the threads here. They also suggested putting a drop of vanilla on the shoulder or back - near the tail - on each cat so that they have a smell that is "the same". This is also something I scanned over, so check it out.
Don't give up on your kitten and take it back just yet. Give it some more time and don't worry too much about your first kitty. She will get used to things being a bit different.
My cats all get along now. Unfortunately, it was a bit different with my non-feline pets (aka kids). I had my second child when my first was almost 4 years old. My first decided pretty quickly that we should take the second one back to the hospital (since that is where it came from in her mind) because she didn't like it.
Now, they are 18 and 14...and my 18 y.o. STILL thinks I should have taken her sister back.