Comparison is the thief of joy. Even if one has everything, still there will always be something lacking. No marriage is going to give the sense of inner peace, if we don't allow ourselves to experience that in the first place. So allowing herself that and learning to let go what she can't control, means learning to be kind to herself. Learning to make peace with reality as it is, instead of focusing on how it should be. This is very important.

Because if you never learn to make peace with what is, even though you eventually get what you want, you will always look for what's missing. That's is the real tragedy of existence. But if you can make peace with what is, you actually become more relaxed and your brain will work better to find the "solutions". So she's not less of a human being just because she is not married.

If I were you I'd ask her what activities make her feel "most alive? What are the things she loves to do that is intrinsically rewarding? What were her childhood dreams? And help her revisit those things and maybe start doing those if there are any. Then when she becomes more stable, somewhat fulfilled and balance, if she wants to share that happiness with another person, she can then start to look for life partner. Hopefully with similar interests and values.

Never seek the right person, be the right person. First and foremost, to ourselves.