How do I cheer up my depressed roommate?

According to our school's counselor, my roommate has mild depression and thinks it's possible that it might be worse.

She always seems to have problems with guys, and this summer she had her heart broken by her boyfriend. So when the counselor told her that, I think she kind of grabbed onto the diagnosis, because she seems pretty convinced now that her problem is depression.

She acts happy most of the time when she's around me, but apparently she's really upset inside, and just recently she told me that she doesn't find many things fun anymore.

Well, anyway, I really feel bad for her and I was wondering if there's any way for me to help her through this? When we hang out together I have fun and I think she does too, we always laugh so much. But I want her to be able to be happy all the time.
How do I cheer up my depressed roommate?
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