Sleeping Problems

I have a step daughter who is nearly 8 and she refuses to sleep alone. To top it off my husband isn't much help. She cries every time we put her to bed stating she misses mommy (we get her every other weekend) which I get but I think it is time for to learn to sleep on her own. My husband will sometimes lay with her until she falls asleep but she will still come in our room in the middle of the night crying. My husband will let her lay with us and tells her she has to go back in a minute but doesn't make her or just ends up sleeping with her in her bed. I need help in two areas: how do I make my husband see she needs to sleep on her own (he just states I don't understand? Btw our 1 year old sleeps in his own bed) and how do I make it easier for her? I want my husband back and I want her to feel comfortable and enjoy things like slumber parties and such.