Toddler started doing poos at night

[Jane7]

My 27 month old dd has started holding onto her poos until she goes to bed. Usually I go up to check on her at about 11pm and she's done a huge poo. It's not really a problem, except I know she's doing it because she's become uncomfortable doing poos and I'd love to try to change that. She often goes four or five days with no poos, then does a huge one. Has anyone else got a toddler who has done this? We had a vague attempt at introducing potty a few months ago and I think that was when all our problems started. We gave up quickly and now back in nappies, but she just seems to resist doing a poo, then waits until she's got some peace in her bedroom. Makes sense I suppose! Any advice appreciated.

our toddler did it last summer. She would hold on for days and then do a huge 1 behind the curtains with shouts of go away and don't look at me. I have a horrible feeling that we didn't notice until it had become an issue because she was at nursery or with grandparents and I assumed she had done 1. When we potty trained her she held on so long that they got too big and hurt so we ended up in a vicious circle which was really horrible for her. Saw GP and a combination of movicol and good diet sorted her out relatively quickly.
I would keep a close eye and at the first sign of any pain or struggle to poo take her to the docs?