Your cousin sounds like an optimistic person, and I'm sure she wants to encourage you and cheer you up. The Bible says that "A cheerful heart is good medicine"–and that's true not only for the person who is cheerful, but for those around them (Proverbs 17:22).
The problem, however, is that simply having faith "that everything will work out" isn't enough. You and I know that things don't always work out the way we wish they would; sometimes they do–but sometimes they don't. Life isn't easy, and sometimes it brings us disappointment and heartache. In the midst of his suffering, Job rightly said that "man is born to trouble as surely as sparks fly upward" (Job 5:7).
The key, you see, isn't just to have a vague "faith"–but to have faith in God! When our faith is in Him, we know that He knows all about our problems and burdens, and we know also that He loves us and wants what is best for us. We know too that we can bring every concern we have to Him in prayer, and He will hear us.
How do I know this is true? I know it because His only Son came into the world to show us God's love. He died on the cross to save us, and He rose again from the dead to give us hope. Turn to Christ today and give your life to Him. Then commit your problems to Him, and trust Him to help you deal with them.