If Anne could make the best of any marriage to Charles, it may have amounted to more than simply exchanging households. A second opportunity to chose her own life; away from Kellynch and some independence from Lady Russell yet still nearby to her.
I'm not saying Charles can compare to CW for Anne; but Charles & Anne at home may have found contentment and appeared happy as a couple. In my opinion, Anne was right to turn down Charles Musgrove but if she had decided to marry, Charles was a decent match who could offer security and stabilty.
Yet, Anne is still emotionally fragile. She never got over CW. Marriage was a way forward for a woman in JA's time but inwardly, Anne may've continued to dwell on memories of CW in inner turmoil and not found the inner peace she needed.
Perhaps a consideration for her in regard to Charles' proposal.

:)