I like to call these alone times in her crib "time to think." After all, unlike us adults, practically everything she's seen and experienced during the day is new information for her developing brain. I've been told and have also read that alone time is really good for infants and toddlers, because it gives them time to process all this new information.
I often wonder if she uses that alone time in the crib at night to reflect on the day past, and the time in the morning to consider the day ahead. I know her thought process isn't quite as evolved as that, but on some basic level this is exactly what her brain must be doing: practicing with her mouth sounds that she heard that day, making patterns in her head, developing an imagination.
So we'll continue to let her be in the crib. Besides, it also means more free time for us.