Did they do a baseline 24 in the first trimester or is this elevated 24hr at 21 weeks your first? It's not uncommon after a pre-e pregnan y to spill more protein than usual in a subsequent pregnancy. As you mentioned probably due to damage from our last pregnancy. It can be scary to already have a bit of a red flag- remember each pregnancy is different- and it sounds like your medical team is Arcady watching you like a hawk.
The only positive reframe we were given when we spilled early on is that it have us a good frame of reference for later on if it rose (and it did). So knowing where we started (baseline at 10 weeks) we could keep the other raises relative to where we started.
Keep posted as you're able- and one day at a time right?

Lauren