How does one keep a good and godly balance between being a hope and light to the sinner and keeping the church body sanctified when sin comes knocking at the door? We are not to turn away the sinner or new convert and yet we are to portray an image of the church that is holy and separate from the world, to be a standard of holiness to others and a witness to who the Lord Jesus Christ is.
Very simply, when a new convert or one who is seeking the Lord comes to the church in immodest attire, we are to share with him or her in kindness that we would love for her to be a part of the service but we request out of reverence for God’s house and respect for the church members that she return in appropriate church clothing. If she is serious about her place and seeking fellowship with the Lord, she will oblige and not let such a small thing stand in the way of her relationship with Him. She will learn early on in her walk, a place of reverence for the Lord in His House (because this is a good start), and the members of the body of the church will be a witness and an example to her to promote a vision and hope in her.
How she dresses when she goes home, to work or is out with friends is her business. It takes years and years for one to be transformed and renewed in the Lord, in the heart and in the mind to eventually manifest to the outside.
Speaking in kindness and asking her to return gives her the message that we want a better life for her, that Jesus wants a better life for her, it shows that we are not condemning her. It sets a standard in love and protection too.