I have a shemale friend and it took several times for me to be able to take her in my ass as she is thick. What finally worked was when I knew we were going to get together I would use a dildo to open my hole up before the date.
The first time I did this she was able to get all the way inside me with little pain and it was such a turn on to her that she got so horny and fucked me sooo good and hard that I love to have her top me now.
Remember keep it safe.