The critical issue here is probably “who pays?” rather than “who owns?” and if that’s the case, in a two-unit block the difference between lot property and common property is moot.
Look at this from the point of view of the outcome that you want. The ideal resolution would be to upgrade all the electrics including the powerboard and meters etc for the simple reason that these things get old and worn, and dodgy electrics are dangerous.
But if your neighbour doesn’t want to do that, then you have to ask if the set-up is common property or not. The “Who’s responsible” memorandum doesn’t help much as it refers to fuses and wiring in a meter room, or electrical equipment in a lot and serving only that lot.
Your set-up doesn’t fit either of those descriptions but I’m going to stick my neck out here and say the powerboard, fuses and meters for both lots are common property that just happen to be on your neighbour’s lot. This would be especially so if the meters also fed power to common property lighting.
If not, the simplest thing, as I said, would be to get her to agree to a revamp of both systems and just share the cost. But if she is reluctant, now might be a good time to split the systems, move the meter to your property and just look after your own electrics.
The opinions offered in these Forum posts and replies are not intended to be taken as legal advice. Readers with serious issues should consult experienced strata lawyers.