Regarding SIDS, at two, babies are walking, and easily strong enough to turn themselves. It’s only babies under 6 months who are as yet unable to reposition themselves that are most at risk. At two, this toddler would have naturally been changing positions as she slept. This is just “One Of Those Things”, an unfortunate happenstance.
Yes, at age 2, probably just one of those very sad things. Speaking of SIDS, some years back Australia (or New Zealand, I forget) banned fire-retardant chemicals on all baby clothes and bedding. Their rate of crib death plunged.