Dipsticks cannot quantitatively measure - and in pregnancy, they worry about numbers. For pregnant women, below 150mg in 24h is normal, below 300mg is worrisome, and above 300mg is diagnostic for preeclampsia when coupled to two readings above either of 140/90. Outside of pregnancy, 0mg is normal - so pregnancy stresses your kidneys a bit.
In women with a history of preeclampsia they will often run a baseline test of proteinuria so that if you've got a bit of underlying damage (even a high fever in childhood can cause this) it can be considered in later pregnancy when higher numbers are more worrisome. I suspect your dipstick reading is just a good reason to run a baseline.
Any woman with a history of severe preeclampsia is at higher risk of preeclampsia in subsequent pregnancies so of course you'll want close monitoring - like a baseline - but I wouldn't take a +1 dipstick as an indication of much of anything!