How to read a 17-month old?

I post this question as Maia is having one of her tantrums. These tantrums just started this past week. And they are daily. Sometimes twice a day. And they drive me crazy. Not because I can't stand her crying and throwing a huge fit (because I find that part kind of funny, actually) but because I don't know exactly WHY she is throwing that fit, and then I wonder if I am doing something wrong. I think these tantrums are a result of her not getting her way. If she doesn't get her way, then all heckaroo breaks out.

Example # 1 - A few days ago she and Noah were coloring. She decided to take a marker (washable, but still . . .) and color her belly. So, I took the marker away, told her she can't do that, and put the box of markers on the fireplace mantle. She broke out in a bloody murder fit. she threw herself on the floor, tears streaming down her face, rolling all over the place, screaming, and hyperventilating a bit. She wasn't hurt. She was fine. Just wasn't happy with not getting her way. I kept time, and this went on for 20 minutes. Yes, 20 minutes. And I just ignored her. (That's what I am suppose to do, right?) Noah even ignored her like he does every time she does this. (There's moments when he even says "it's okay, Maia . . ."). So my question is, how long will this behavior last? Is it a normal stage in baby girls' lives?

Maia has these tantrum fits if she doesn't get what she wants, if it's time for bed and she doesn't want to go, just to name a few. She's even started throwing them because of really miniscule things (not miniscule to her, of course) like being done with dinner, not wanting a certain type of food, wanting to try this or that herself (because she thinks she can do it like big brother Noah), wanting to try and pick out her own clothes (again, like her brother does), wanting to go outside when the rest of us aren't ready to, and so on. (And I let her pick out her clothes, for example, but she gets really frustrated in that process. Maybe the problem is that she can't explain what she's wanting and how she is feeling?)

We never experienced this with Noah. I think he has had maybe 5 tantrums ever. Maia, she is obviously a completely different human being! And one very strong-minded, determined baby girl. (Mom said I was similar to this, but I didn't have any older siblings and my way of saying it had to be my way or no way, was by holding my breath!)

So the question of the day in our house is, will these tantrums end? And is this behavior because of Noah being bigger and she wanting to be like him but she knows that she cannot? What can I do to help her? I need other mommies to help me. This is a whole new world to me and not a world that I find myself comfortable in. At all.

Edited to add this afternoon thought: I just put Maia down for her nap, which she use to go down for so simply. All I had to do was lay her in bed with a drink, her blankies, and wish her good night. She'd fall asleep without a peep. I just attempted the usual easy nap routine, and it didn't work. As soon as I set foot in her room, she threw her head back and almost hit it on the dresser. (sigh . . .) Then I put her in her bed, she stood up, flailed her arms in the air, then fell down on her chest and face. I walked out and of course she's still screaming. Ohmygoodness! What is going on?! I don't think she is teething and I know she is tired. Where oh where did my sweet quiet obedient little girl go? Someone please tell me this is normal!