you both have to be on board with it, and resolved to see it through. first decide what accommodations you ARE willing to make for her (nightlight, music box, white noise, monster spray, nightmare-banishing windchimes, special stuffed animal etc) and let her know beforehand what the rules are.
then stick to them.
every single time she comes into your room, take her back to bed. if she tries to talk to you about her dreams, gently tell her you will listen in the morning and don't engage. let her do whatever ritual you all decide is appropriate to banish the bad dreams, but don't let the episode get prolonged in any way. little to no conversation, not even eye contact, right back to bed.
it may result in zero sleep for a while. but it won't take long for a child this age to get it, so long as you are clear and consistent.
it's okay that she gets a family bed at her dad's. family beds are great so long as everyone is happy with it. kids are very adaptable and able to understand that different households have different routines.
a new toy might be a nice thing to do as a long-term reward (if she's able to do it for several nights running, say) but it's unlikely to be a sufficient motivator on its own.
above all, don't get angry with her. whether the dreams are real or a ploy, sleeping alone is clearly an issue for her and you want to help her cope with love and compassion. it's hard to do when you're sleep-deprived, but hang in there.
khairete
S.