She Has to Leave Behind Everyone
The sad reality is that it is not only Alyssa who has to sacrifice for her dream. Her friends and family also must be willing to accept that they are likely never going to see her again. Currently, technology would not allow people to return after a prolonged stay, meaning that the first settlers are likely to be forced to stay on the Red Planet. Even Chris Hadfield admits that it is unlikely that the early settlers can ever make it back to Earth.
The Risks Are Numerous
Even ignoring the fact that it is unlikely that they can even return once they make it to Mars, the early settlers will also be in danger from the start. As we have learned over the last several decades, the smallest malfunction can cause catastrophic failure in a rocket. This means that the risk of dying before even making it to Mars is extremely high. Once she makes it, there are even more risks to be concerned with.