Should I feel taken advantage of money wise?

My classmate is an avid hiker and I've developed this love for hiking as well. One weekend, I reached out to her and asked if she wanted to do a city hike with me. She was down but wanted to do one further south because she was having dinner plans in the area. It was important to me to go hiking so I said ok. She picked me up, took us there, hiked and dropped me off at the bus station because she could not take me back. I was fine with that but she also asked me to trip in for gas. That bothered me but I gave her the estimated gas cost for my share of the one way trip. I felt upset because I feel she would have driven down to the area for dinner whether or not I went along with her. Do you think it was proper for her to ask me for some gas money? I understand gas is pricey but it was not like I asked her to drive out of her way to go hiking. I feel it would be necessary in that case. A similar scenario happened this weekend - she decided for us to go south again to hike because she makes these monthly trips to these discount stores. I did get to shop for groceries and clothes with her and she took us back into town but she asked for gas money again. I begrudgingly gave her a few dollars. I'm conflicted. I enjoy hiking with her. Hiking buddies are hard to find for me and I do not drive which makes hiking hard to do without a car. If she does not drive there is no way I can really hike outside of the city. Should I trip in for gas every time even though she decides where we go and it's at her convenience? I feel taken advantage of money wise and bothered but I can't tell if I should be feeling this way. Please give me your honest opinion. Thanks!