The gentlest method to get toddler to sleep on her own?

[TigerQuoll]

Sister 1 has a 2, nearly 3 (October) year old daughter, and sleeps with her every night in a double bed. She's trying to think how she can get her to sleep on her own but she doesn't want to do cry it out because she thinks that just teaches the child that no one will come if they cry. She is a little jealous of Sister 2 whose 2.5 year old daughter has slept well on her own since 1 year old as they did sleep training at that point (except recently she started getting up at about 3 in the morning to come into the parents bed but they got her a gro-clock which she understood right away).
Daughter of Sister 1 will cry if she wakes up and no one's there - I babysat last night and lay with her until she fell asleep but she woke up when sister 1 and husband came home and started crying because nobody was there.
Anyway, what methods can you suggest she try? Any good books?

Is the toddler open to bribery? Whole night in your own bed you get a sticker/or something. A whole week of stickers and you get a toy you want.

Oh yes she is - she has been toilet training and asks for a smartie every time she goes. I'll suggest that!

Depends how urgent it is to get the child into her own bed, I guess. We co-slept and let dd move to her own room when she was ready. If I had wanted to speed up the process, I'd probably have started having conversations with her about when she would be ready to move into her big-girl bed, and perhaps taken her to buy some special big-girl bedding and maybe a stuffed animal to keep her company, perhaps a special water bottle to keep next to the bed or a nice nightlight if she didn't like the dark etc. Essentially, I'd have tried to make it seem grown up and appealing to her, and to address any potential fears or concerns

It will need to be gradual and will probably need someone to gradually retreat at bedtime so child falls asleep on their own. Cosleep if little one gets upset or try to resettle

DS has improved hugely and sometimes I wake in my own bed. He is often much better if we've done night night blow kiss and left the room but while DH always can do that, I can't always