At their own pace and in their own way. Help them to heal and understand themselves better. Encourage them to take time by themselves and give them the space they need. Help them cultivate strength. One way to encourage growth is to give those you love the freedom to love others.
Some people find neediness and weakness very attractive.
Maybe they think they'll be abandoned if their loved ones get strong. They might give generously but with conditions and strings attached. Growth can be stunted by difficult emotions like insecurity or fear of abandonment. One way to manage a limiting emotion is to meet it head on. The only way out - is through.