I was 8 weeks pregnant the last time I went to Disney
(2006) and it was fine. I had some morning sickness, but it wasn't unbearable and didn't hold me up.
Yes I didn't go on every ride, but there was plenty to do. Of course all the theater-type attractions were fine. And I believe I did POTC - the drop in the beginning isn't pretty small. Haunted Mansion, Great Movie Ride and such were also fine.
I obviously didn't do any thrill rides, but was able to wait on line with my husband and then went out the "chicken way" when he went on the ride. I also didn't dot he safari in AK as the roads can be very bumpy and I didn't want to take any chances as with the backlot tour and castrophe canyon.
The only ride I didn't go on because I wasn't feeling up to it was Soarin'. At the time I was nauseaus and was afraid the feeling of movement and such on Soarin' would make it worse.
I went in Feb. so didn't have to worry about the heat. But of course you should be well hydrated. It was a special trip for me as I felt it was the first time I shared the Disney magic with my baby. I bought some special souveniers for my baby - My First Disney Bear is now one of his favorite stuffed animals and he sleeps with it every night. DH was wonderful and understood when I needed a rest and didn't mind going on some of the attractions by himself. I had been to Disney many times and this was his first time in a very long time and I didn't want him to miss out on rides because of me. We all had a wonderful time.
The only suggestions to your friend is to first make sure she gets
trip insurance. Being pregnant you never know and just in case she can't go for medical reasons she will get he money back with the trip insurance. Also, she should of course check with her Dr. and make sure everything is OK for travel. I flew (from NY to Orlando) and was fine.
It shold be fine for your friend to go when she's pregnant and there will be lots for her to do. But it should be up to her. If it's her first pregnancy and she's not sure or uncomfortable with the idea of going, then there's always another time. But for me it was very special being pregnant at Disney - I had lost 3 pregnancies before this one and I felt sharing the Disney magic with him was good luck.