That can be a very difficult question to answer for many people. The idea is probably to get you thinking about what is important to you, including any goals you have for therapy and your life, so you can start moving towards meeting them. It's likely to try and help you feel more positive about your future and pinpoint specific things to work towards. But it's one of those questions that can invoke more of a sense of desperation and - like you said - failure, if it's enough just trying to cope with how life is now. It reminds me of a question my former T used to ask a lot 'What would you ideally say to such and such?' I knew full well that saying what I'd ideally say would never be an option for many reasons so it just made me feel awful.

Asking about your future in 5 years can help some people. If it's not going to help you, tell your T so. She should then be able to re-adjust her approach and stick with what you want to focus on at the moment. Maybe later on you'll feel more able to think about what you want for yourself in 5 years.