Be forwarned that people on DS seem to have very strong opinions about sleep training. Hopefully everyone can keep it civil, but this thread may turn into a CIO-bashing. Let's try to just help this mama politely
Yes, I think she is too young for the type of sleep training you are describing. Most sleep experts say no younger than 4 months for cry it out (CIO), simply because it is pretty ineffective. However, the "evidence" that a lot of parents cite about the psychological harm of CIO is, well, simply not there. A lot of websites and books, including those by Dr. Sears and others, are citing studies that cite experts that cite studies....and on and on. It all looks very legitimate, but the actual peer reviewed studies themselves (found in published journals, not websites or parenting books), if one takes the time to sift through them all, have NOT found psychological harm from CIO in a loving family with otherwise attentive parenting.
Okay, now that that is out of the way, I have found a couple of pretty useful tips that I refer to as "sleep training" that I use straight from birth:
-I try as much as possible to put baby down when sleepy but still awake. But sometimes I snuggle them to sleep anyway. They are so squishy and yummy
-I try to wait about 5-10 minutes after baby starts crying at NIGHT before rushing in to nurse. Very often baby is just being noisy (sometimes very noisy, eyes open and everything), but really just transitioning between sleep cycles. Rushing in to soothe her may actually be teaching her to fully wake up between cycles, instead of learning to ease between them on her own.
-I NEVER let a newborn go more than 3 hours between feeds during the DAY (4 hours starting around 4 months). Meaning, if she takes a 3 hour nap during the afternoon, yes, I will wake a sleeping baby. I try to make them take as many calories during the DAY. Baby only needs so many calories to thrive. If she gets most or all during the day, she has no need to wake at night
-The limiting of their naps to no more than 3 hours during the day also ensures that they don't do all their sleeping during the day and waking at night. They are good and tired at night.
-I try to feed baby upon waking, rather than nursing to sleep. Like your article said, babies tend to sleep best when they fall sleep on their own.
-I try to limit awake time to 90 or so minutes at a stretch during the day, between naps. Beyond that, most tiny babies get overtired and do like you describe, can't fall alseep on their own and get really fussy when left alone to sleep.
-I try to not worry too much about waking older kids. It is hard to not jump up to quiet them at night, but truly, most kids will learn to sleep through it. Plus, older kids are easier to put back to sleep IME. A white noise machine or fan may help block the crying for your toddler.
-I don't cosleep or co-room. My babies seem to smell me and wake up to nurse more when we tried that. We all sleep better in our own rooms.
-Flexible routines are my friend, but it didn't happen until 3-4 months at the soonest. By then we were usually doing 3 naps a day with feeds every 3-4 hours, with a total of 4-5 feeds in 24 hours.
Three of my four kids were sleeping through the night (totally and completely, no feeds at all for at least 10 hours) by 12 weeks. They did this on their own, without any CIO, and two of those three were totally breastfed. My third child was a spitfire and woke at night until she was almost 2 years old. Nothing works perfectly for every child.