Nearly four year old potty training disaster HELP

[twinklecow]

To be honest DDs potty training has never gone well. Tried gently a couple of times, but seemed ready at 2 3/4. Went ok, but never really progressed to asking to go independently and most poos in nappy. About 4/5 months in started asking a bit more (but still with lots of prompting). About 7 months in she started a new nursery, ok with a couple of accidents but about a month in it went completely backwards, poo and wee accidents daily as well as some at home.

We tried lots to help, but also saw a counsellor who advised stepping back. Wees got better overnight and hardly any accidents, but at the same time started withholding poo. Have been treating with Movicol for past few months and progressing ok with regular poos in nappy/ potty. About a month ago it all went backwards again, wee accidents daily at home and nursery, withholding poo.

Am at a loss of what to do next ? Any suggestions ? Any stories of hope ?