Potty Training Question for child with potty issues

Soon 2 be Lockhart

I have a question that I hope you guys might be able to answer. But first a little information:
I am a first time mom
My DD is 27 months – born 9 weeks early
DD has a fused labia (since 6 months) but has had no uti’s , we tried the estrogen cream at 6 months (worked, but then sealed shut again) and then again at 24 months which only opened it up a small amount and then closed up within a week after stopping. I apply vasoline daily to help. She gets very irritated in that area and will cry and ask for the cream (vasoline) her doctor says it is from her urine getting trapped, so I try to keep it as dry and clean as possible.
DD has bad constipation, she is on meds for this which helps some, but we still have issues with it a few times a month, to the point she will cry for hours because it hurts and even vomit do to her pushing to get it out this will last a few days until she can finally push it out. This has caused skin tags that can break open and bleed during these episodes. Unfortunately until we get the constipation under control her surgeon will not remove them because the constipation is what is causing them to be there, so they will just continue to come back, she currently has 3 of them. This has been an ongoing problem since she was born.
DD will tell me when she is going pee and poop. She needs to be changed immediately (usually she is still going when demanding to be changed) and will do it herself if you are not fast enough. This has been going on for 3-4 months now.
DD can dress herself with the exception of long sleeve shirts.
DD wants nothing to do with the potty chair or toilet. But she will insist her piggy go potty on her potty chair all the time she even wipes him and then flushes the tp when done.
I feel she is ready to potty train, with the exception of pooping only because of her constipation issues. But how do I get her to sit on the potty chair. I will ask her and she tells me “no” if I place her on it she will become very upset and that is not how I want to train her. I have offered her m&m (her fav), just to sit on the potty but she still says no, I have tried to move the potty into the living room with the tv, but she becomes upset that the potty is in the wrong room and will pick it up and take it back to the bathroom. I know in time she will decide to us it, but I think if I can get her into underwear it might help her labia (at least that’s what her doc says). Personally I am in no hurry to get out of diapers, I am not looking forward to the 50 potty breaks she will decide she needs when we go out, but I do think having her in underwear will help keep her labia dry and less iterated.
Does anyone have any suggestions or do I just need to give it more time.
Thank you for taking the time to read this, sorry it is so long.

*LrCg*

First, I would gather to say her fear of the potty is the pooping issue and justifiably so (not to mention the labia issues).  I know you say you've been to a doctor- is it your family doctor or a GI pedi specialist?  My friend she had to have her child see a GI pedi specialist and they did an adult dosage of Mirlax for 3 days to clean them out and then slowly over months decreased it and the child had to stay on it.  A GI pedi specialist would have more and better information than a family doctor/pedi.  I think once you get that resolved you will have a better chance on tackling PT.  Also, remember that your child is now 2 and they are in the middle of the "no" stage (generally @20 months to 2 1/2 years old) so everything will be a power struggle and I'm certainly not implying your child is "bad" (all children at this age are in the "no" stage) but I would recommend that you have obedience/respect so when you say its time to sit on the potty they respect and listen to you.  I can understand where you think PT would make it easier for her but I think her fears are understandable and if you tackle those first (not that you are ignoring them now) and work on listening skills and the natural power struggles that occur now you will have more success.