R.R.
Good for you, Mom! Here in the US we let our children make the decision when they will be trained so often ignore the signs they ARE ready and have struggles later.
I imagine that public restrooms are just not familiar to her like the one at home, and think it may just take awhile for her to get used to them. Being only 20 months the regular toilet may seem huge to her as it does to my 27 month old, so I'm planning on getting this folding seat that's cushier than most, says it won't pinch and is affordable.
http://www.pottytrainingconcepts.com/Cushie-Traveler.html
The concept of pooping does seem to take longer, it did with my daughter, and one thing I've found that helps is taking her in the bathroom when you go and having her sit on her potty at the same time, so she sees you doing it all from sitting down to washing your hands. And, I believe it will just come naturally from observation and increased awareness of her body's sensations. You're 4 months away and she may get it by then ; )