I'm going to agree with London. I think this situation, on her end, could be stemming from three very different places. A: she has everything totally together, especially regarding her emotions and the amount of support she has as a brand new parent, and she has just been sitting on these feelings while she has been busy being pregnant, and that things are ready to go swimmingly OR B: she is at the end of her rope, especially after having to still feel like she needs to present herself as totally together and independent and awesome after becoming a single mom to an infant, and more than anything just wants the emotional support she sees in the relationship between you two, and sees offering herself up in a relationship as the only way to get that support without having to admit that she is feeling vulnerable OR C: a sort of mix between the two (which is probably the most realistic of the three options)- she might have been sitting on some feelings for awhile, needs some support with this new challanging aspect of her life and sees you guys as a great resource for that support, and she is feeling like it might be a good time to explore that as an option.
Here's the thing for you guys to remember: she just had a baby, and hormones are still going to be wacky. She also probably feels weirdly vulnerable in ways she most likely won't admit, given your description of her, and quite honestly needs a strong support system at this time. I hope for all of your sakes that feelings are real on everybody's part and that this could be a beautiful thing for everybody, but as her friends who think she is as wonderful and amazing as you say you two do, first off, be FRIENDS to her and her baby. Reach out to her as friends, not as potential lovers, to see if she needs help with the baby: errands run, a break to rest, some relaxed company. That being said, after pregnancy and a newborn, especially as a single mom- she is probably also yearning to feel like a desirable woman again. So, a little romance would probably go a long way- flowers, an opportunity to dress up, that kind of thing. Also, I suggest some quiet one on one activities with her and each of you alone that would prompt a lot of talking regarding feelings and emotions and boundaries at this time. Personally, I like spa trips for this kind of thing- you're together and relaxed, but you can't turn it in to a physical thing, so more emotional stuff comes out. Basically, treat this gently, with respect and caution, and you might have something really great- if not, there would probably be quite a bit of regret sooner than later. Slow and steady wins the race