while she had to wear shorts that went past the knee in Syria, in Jordan she wore regular shorts, and was fine
In most ME countries there is a decisive difference between what is acceptable for a local girl and what for a tourist. In a well-visited touristy area like Petra or at the coast of the Dead Sea you can get away with shorts and strappy top, but that doesn't mean you should dress like that.
I best tell you about an encounter I had in Aswan, Egypt.
I was waiting in front of the Nubian museum. I am muslim and was dressed accordingly, but you could not mistake me for an Egyptian, my mix of European streetwear clothes was just too different. So I got some curious glances from a group of 15-17 year old Egyptian girls who were there for a schooltrip and finally heard the familar hissing: "Ksst, ksst." It is the discreet sound girls and women in the ME use to draw attention to themselves when they want to strike up a conversation with a stranger.
I turned around, looked at the girl who had hissed and she asked shyly: "Takhki Arabi?" (Do you speak Arabic?). We ended up having a halting conversation in a mix of English and Arabic, mainly along the lines of "where are you from, how old are you,..". One of the girls told me her brother was a student at "Deutsche Schule Kairo" and was planning to study in Germany. She was envious of him and wanted to come to Germany too, so I gave her a bunch of addresses and urls that would be useful to her and her brother. I also told her she could work as an Au-Pair with a German muslim family, there are always some that are specifically looking for an Arab-speaking Au-Pair. I found it very nice and refreshing to talk to these girls and as far as contacts with locals went it was definitely one of the highlights of my trip to Egypt.
The point of this story is the following: ME girls have to be very careful about their reputation. A nice respectable girl from a conservative lower class simply doesn't talk to tourists unless it is necessary for her livelyhood. They would not have approached me at all if I had dressed like a typical tourist tart, but as fellow muslim woman I was safe to talk to. I know that because I had similar encounters in Jordan and Palestine.
So if the difference between a tourist and a traveller is that the traveller takes an interest in the locals and is respectful to their culture, it most definitely makes sense to dress accordingly. Cover yourself from knees to shoulders at all time and if you want to err on the side of caution cover ellbows, shoulders and all the way down to your ankles.
I read in hotels in Iran and/or Syria, they have a tendency to hold on to your passport.
Yes, because they have to register you with the police. But showing them your passport when you check in and handing them a copy of the data page should usually be enough. Sometimes they'll want to see the visa too and may also need a copy of it. It therefore makes a lot of sense to have about 10 copies of the datapage of your passport with you. These copies are also useful in another case: there have been incidents when foreigners were accosted by fake police in a bid to get at their passports. So if the police stops you, hand them a copy first and tell them you have the passport at the hotel.
Is Jordan quite conservative too?
Yes, because many Jordanians are ethnic Palestinians. For them being muslim is a question of personal honour, they take great pride in their deen (their faith). As such they support conservative values. That they share a border with Saudi-A. only increases this tendency. The official name of Jordan is "Hashemite Kingdom of J.", the Jordanian Royal family derives its right to rule from the fact that they are descendants of the same tribe the Prophet Muhammad belonged too. As such they rule with the clerics, not against them. Syria on the other hand is run by the socialistic, nationalistic and pan-arabic Baath party, the government seeks to diminish the power of the clerics and establish a secular state.
was thinking of going into Jordan for a bit too..
If you really want to visit Turkey, Syria and Jordan the best way will be to fly into Sharm-el-Sheikh in Egypt with a cheap charter flight and then travel overland from there to Istanbul.