You ... get used to it. Familiarity, is, as mentioned, the key - narrating the location and why it should be familiar and when they moved there and ways they can prove it's theirs (e.g. keys fitting the front door) tend to help quite a bit. A dissociated mind still wants to believe it should be where it is and that that makes complete sense, it just doesn't have the data available. Eventually, with luck, you can get…
Wouldn't something like polaroids be a good strategy, you know, like in Memento? When she forgets everything, have her grab photos from her bag, one together with every person she trusts, one of her in front of her building, one of her in front of a street sign for her neighbourhood. Also, a pocket mirror if she really forgets who or even what she is.
Grounding is a common method of dealing with anxiety and other mental health issues. The idea of finding your place, finding familiarity, centring yourself. Something you are very used to doing normally and when safe is important, as is having that also associated very strongly with being safe.
For some people, photos will work well for this - they might capture moments with strong association with safety and happiness. Some people may be able to instead use an object, a talisman of sorts.
For others, or for when the disassociation is worse, a single grounding method may not be enough. It's about building the complete story - getting home and watching something familiar. The grounding only happens from weight of evidence.
Finally, there's something you don't hear talked about much. Coming back around from disassociating can be utterly terrifying in it's own right. Both as one tries to return, and after coming back. Having multiple entirely different means to ground helps with this.