Your daughter isn't too young to train.
First pick a word to use in your house for going to the bathroom and start using it. Let your daughter go into the bathroom with you and her older sister and use the word of choice. You daughter may know she's about to go but doesn't have the word yet to tell you.
Also watch for her cues. She may be telling you non-verbally that she is about to go. She may get quiet all of a sudden, or stop playing and go off by herself for a little while.
You can also let her go naked for a day and try to watch her that way and also catch her and get her on the toilet.
As someone else said when she wakes up would be a good time or maybe before bath while the water is running just try putting her on the toilet.
If you don't do the potty chair you can buy a potty ring with "Blue's Clues" on it or some other character that will fit right on your seat.
And get a stool. Even if they can get themselves on the toilet its much easier with a stool as well as getting down.
If your daughter doesn't stay on the toilet long enough to actually go, or is too excited to let it happen, give her a toy or book and just hang out with her on the toilet.
I would also make a big deal out of her big sister going.
Also once my youngest started going a few times on the toilet I brought her to
Walmart to pick out some character panties. She really wanted some since her sister had them. She would wear them over her diaper. She figured out all on her own that they didn't belong over the diaper and she would ask to wear them without it. I would allow her to, but I told her that she needed to keep "Dora" dry. It seemed to work.
Its tough, with my oldest I did train her and she finished just about her 3rd bday. With my youngest she trained me and was dry day and night just before she was 2. She was ready all on her own and I have been trying to figure out what I did differently. And all I can come up with is that her sister was being trained and newly trained pretty much her whole life and therefor she grew up with all the lingo. They are only 20 months apart. I put off training my youngest because I felt like I just finished with the oldest but I guess the no pressure technique worked.
So my biggest advice is to be patient and just go with the flow. She'll get it.