I believe one of the most beautiful things about marriage is that both of you do change as people--but that you change together, and hopefully to bettering one another as well. It is perhaps most realistic to expect changes of goals as a person grows, matures, experiences new phases of life--that's just how people work. The trick is the growing "together" so that, as you change and grow, more and more your thoughts, actions, and goals are considered in light of one another.
When it comes to practical things as you mentioned, I think there are ways in which new goals are good, but can be achieved together, or perhaps not in the way you thought or would have done as a single person. (You've got to be creative sometimes!)
An anecdote from my own life to perhaps illustrate: I recently decided that I wanted to return to school to complete my undergraduate degree, but also in a field that I had not previously been in when I first set out to school. I had changed a lot in the time since high school and now, and I had come to re-affirm a new (rather, an old but resurfaced) passion. My husband was quite supportive, and so in the past year I have been going to school. This inevitably means that there are new things, and new opportunities that have come up that I might have jumped at if I had started the endeavor much earlier, pre-marriage, but also I find that the key is not to look at superficial, specific goals, but to satisfy those passions which are inner-goals, not necessarily dependent on the specific scenario. What I mean by that...
First example - Finding local/nearer means to achieve the same goal--that benefit and work with your current situation
For example, I am a biology major. One thing that I have learned since delving into my 'new' passion is that I love wildlife and ecology research and field work--I love working with critters, and learning about them. I have had some opportunities (and there are many fold others) to go a great distance and do intense internships--but doing them would be hard on both of us to be apart for so long, and might tax me. And yet, I love the 'doing' of science. So instead I have sought out local opportunities to be active in this new thing that I love--I am now part of 2 research teams and am hoping to be a part of a citizen science project involving box turtles in the southeast (turtles and tortoises are my passion!). In this case, there were alternative, closer or simpler means to 'do what I want' without sacrificing strain on our relationship.
Second example - Seeking out the 'heart' of your passion, and finding what 'scratches that itch'
Second example might resonate well with your friend. I, too, have always felt a passion for the mission field and reaching and equipping people, not just with the Gospel, but with practical aid and knowledge. When I was younger, I thought that meant becoming a missionary and going to other countries, but as I have grown, I have realized that the root of that passion is in meeting the lost, and encouraging people of want by meeting their situation. So instead of going to another country, I have sought out local ways to get involved with people. I am looking at perhaps getting involved with helping underprivileged people in my community, and also teaching to GED students, as well as getting plugged in more with church evangelizing and missions efforts. There are a whole host of things that can satisfy the soul of someone with a heart for missions -- working with young women (most disadvantaged) at a pregnancy center, or working with groups that help women/children in abused, or trafficked situations, feeding the poor with soup kitchens and food pantries (you don't have to *own* one to be involved with one!), tutoring young children or adults seeking GED or higher education, volunteering at old folks' homes, being involved with immigrants by helping with housing/accalamation needs or ESL learning, etc. I think the heart of a missions-minded person is reaching the lost, and while it sounds like a 'disappointing' or 'unglamorous' approach to say "we can do missions in our own backyard" -- the truth is that we CAN. If you don't start where you are, with the resources you have, how then can you learn to enjoy and utilize plenty?
Another thing is that you can also be involved with global missions and charity work also. There are many economic, social, and other such efforts that lay people can get involved in--whether that's sponsoring a child or a poorer person in a village, buying a goat or a calf for a family, sending resources or other aid, getting involved with internet language-learning to help others, becoming a host family for international students (of all ages), and more! It is so much easier in the world we live in to be present and active participants in missions work. For me, I have found that the romanticized notion of "having" to go oversees to make a difference in people's lives--even people in the third world--is not the real heart of my goal, and that really it is a love for Christ's creation. Therefore, I can find ways to be a part of it wherever I am (and, yes, it IS just as satisfying to me, and I have no regrets).
Marriage doesn't have to mean that you have "hindered" goals per se; instead, it can mean that you have new goals--new goals that you don't have to accomplish alone, but with a partner and constant encourager beside you, new goals that reflect who you are in your time and place, and with the providence that God has shown you. There are many things that we cannot change about our situations or ourselves, but if our ultimate goal is to love God, to worship and enjoy him forever, all other passions and goals in life that are worth following will be in accordance with that.
