Growing up, my mother always made me one of my favourite treats, which was arroz Guizado, or Spanish fried rice. It was the only kind I had ever tasted up until I was around eleven or twelve. When I went to visit my friends' houses, and if they had Mexican food that I didn't like, they offered to give me whatever leftover Spanish rice they had. I immediately noticed the difference: it was rich and flavourful and perfectly balanced, plus it was a little bit creamy. I recently got enrolled in my state's independent skills-training programme because of my blindness and other disabilities, and my skills coach and I found a basic Spanish rice recipe that had the following:  2 US cups of rice 1/8 cup of vegetable oil 6 stems of cilantro (optional) 1 tsp salt 1 tsp minced garlic 4 cups water with 1 cube chicken bouillon or 4 cups chicken broth and no bouillon a dash of cumin to taste a dash of garlic pepper to taste  We started by browning the rice before adding the minced garlic, letting it saute for about a minute. Here's where things get a little weird. I will differentiate the different method that my mother did it versus how my skills coach taught me to do it using A for my mother and B for my trainer. I told my mother exactly how to follow the directions, but being blind, she could've done something that I couldn't see. A. Let the rice fry (with onion) for about five to ten minutes until they are really dark before adding the tomatoes. B. Let the rice and garlic fry for about a minute or two before adding in the tomatoes. A. Since we didn't have any tomato sauce, we blended the tomatoes thoroughly and poured them into the rice. B. Boil the tomatoes until they are soft and mushy, and then mash them up thoroughly before pouring it into the rice since we didn't have any tomato sauce. A and B. Add the bouillon cube and spices. A. Pour four cups of plain water. B. Add four cups of the water used to boil the tomatoes so as to add more tomato flavour. A. Cover the pan and simmer for about fifteen to twenty minutes (this is where it starts to smell strong). B. Cover the lid and let simmer for about forty-five minutes (doesn't smell as strong). The result is that the rice my mother made has almost no flavour, tastes like cardboard, and has a weird smokey-like aroma to it, whereas the one my direct support provider and I tastes much more palatable, has a creamy texture, and feels much more fluffier in general. When I asked my mother why it had that strong aroma, she simply claimed that it was the onion, but I don't think that is the case.  could overfrying and/or undersimmering the rice caused this to happen?  If not, what else could've gone wrong to cause such a thing to occur?   
The simple explanation is that your mother regularly burned the rice.  That would cause all of the off flavors you mentioned.  The fact that she says it should be "really dark" would indicate that it was.  She may have burned the onions as well. Mexican tomato rice is often heavily fried before boiling.  However, it doesn't change color much -- maybe a tiny bit of tan in spots.  You mostly have to judge whether it's ready by smell; the rice starts smelling "nuttier" and then you know it's time to add the tomatoes. For example, here's the instruction from Mexican-American chef Pati Jinich's recipe for red rice:  Heat the oil in a medium saucepan over medium-high heat until hot but not smoking. Add the rice and cook, stirring often, until the rice becomes milky white, 3 to 4 minutes.  She's frying it for longer than your instructor did, but you'll notice it's still not "dark". 