My daughter 3 and son 1.5 went through this cos they thought it was funny when i yelled. I would say its attention seeking, They decided to spread the poo all over my brand new fridge.  They did it about 3 times then stoped so i hope your daughter stops. Try telling her its yucky and she will get sick. Good luck i know how gross it is to try and clean the mess.

You wouldn't be the first mother whose toddler is fascinated with playing with poo, lol!  However, it does sound like a bit of jealousy thing. My suggestion is to not overreact to these regressions - they will pass when she feels more secure.  Just treat it like you do when she has a night time accident.  She either can't help it (toileting regression is very common when new babies come along) or she's doing it to get your attention.  Either way, treating it as no big deal is your best option.

Some things you can do to reduce the jealousy are a) get her involved with caring for the baby (ie. help with bath time), b) when baby is asleep or daddy is home, take a few minutes to do something just with your daughter, like play a puzzle or even have a bath together, c) develop a special routine and ritual with her, like a bedtime routine and a funny nickname that's just for her, d) get daddy to develop a daddy-and-me routine with her,too.  Can he do the bedtime read, for instance.

Good luck!