well of course you know her, and I don't...

and if your gut has a good feeling about this, I'd say go for it....
Here in New Zealand we don't have a time limit on how long a birth mum can take to change their minds; but the earliest they can sign over parental rights is 10 days post birth. And if she's old and wise enough to have known that the adoptions were right for her babies, that's a huge step in the right direction as far as you're concerned...
'Our' birth mum had just turned 16 when she birthed, and her own drug-addled dad turned up out of the blue and pressured her to keep the baby. Her own Mum ended up adopting the baby, though she'd said for months that was the last thing she wanted to do...
So my opinion is undeniably coloured by this experience.
Keep us posted; interesting times!