Downscaling Seems Off
My guess would be that she is alot higher than that area and has more abiltys and passive effects to utilise therefore she may have alot more stats reduced because of this see how it is in a higher lvl area you may end up seeing this happend to you and not her.
Scaling (both up and down) just seems to apply a simple multiplier to your stats. The algorithms for scaling is going to assume level appropriate gear. If you aren’t then you will be significantly weaker. Additional issue that is relevant here is that starting from lv65, gear switches from 2 stats to 3. The game is going to assume you have the stat points from that 3rd stat. If you don’t that is going to be a big chunk of missing stats.
See attachment for an example of going in the opposite direction(due to a bug).
Assuming simmilar builds,skill and gear stat distribution, I think (not sure on this) that it has to do with the equivalent level quality of the gear depending on level.
For example, at level 28 the best gear quality you have access to is masterwork (green), so if you have all green gear you already have the best quality you can get. Your girlfriend, at level 65 has access to rare (yellow) gear, so greens are a step below of the best gear she can get. I think the downscale system takes that into account.
wrapped up in some crazy ritualist hoo-ha from Cantha.
A real grab bag of ‘you can’t hurt me. They’re called Guardians.