I think this time you should let her in your bed, purely for comfort's sake.
However, I don't think you are at all unreasonable for wanting your own bed back, your partner moving in has just brought the issue to the forefront. It's really tricky though, obviously you're not going to tell her honestly about why you want to share a bed with your partner so you need to come up with a simple, understandable reason that she'll accept and be happy with, and not take as a rejection or a wedge between you. Easier said than done! I'm not really sure what you can say.
Maybe for now the focus shouldn't be why she can't share your bed but rather why it's so much better for her to stay in her bed. Could you do a little revamp of her room perhaps? New sheets, curtains, bin and rug, all her choice. Picture for the wall?
Focus on her, keep reminding her how loved she is, how special she is, how no matter what you'll always be a team. She's not losing anything by your partner living with you, she's gaining a friend and maybe one day a step parent. Keep telling her that. I'm sure she will get even closer to your partner after he moves in but the change is going to be a pretty monumental shift for her to wrap her head around right now.
Be as gentle as you can be with her but it's fine to have some boundaries and your bed can be one of them. Perhaps you'll have to sleep in her room for a night or two when she's next poorly as a way of bridging the gap between open bed for her and no sharing at all. Let's be realistic though, it's a relatively short time until she's a teenager and far less likely to even want to share a bed.
Be kind to yourself. It isn't your fault, you've done nothing wrong! It's a lovely thing that you've always done this for her, it's just a natural conclusion to this part.
Oh and congratulations for the big move in! Exciting times!