YAAAAYYYYY!!!
Whistles!
Applause!!
WOO HOO.
You were in the right place at the right time.
If she's usually pooping at about the same time every day,
you can try putting her on a potty (or kiddy seat on big toilet)
at about that time each day and encouraging her.
HOWEVER . . . . this may have just been a fluke.
If you haven't talked about, encouraged, read books about, etc.,
this topic, it may be premature to expect big girl behavior.
Yet.
We had a little book about a little girl elephant and her potty chair.
We had started reading it together around that age,
and my DD figured it out from reading the book
and seeing the (conveniently placed) potty chair.
But if you haven't (yet) laid the groundwork,
it might be unrealistic to expect follow-up behavior.
You know your daughter. Does she learn new things quickly?
If you have a conversation with her about this momentous event,
does she seem to understand what you're telling her?
However it goes, congratulations!
I could feel your excitement and joy all the way here.
About potty chair versus big toilet . . . .
I personally like a little potty chair close to the floor.
I think it's better for independence and safety.
However, if she's comfortable with climbing up using a step-stool,
and you're not worried she'll fall off . . . .