The author spent at best 30 minutes reading wikipedia about Europe before writing this. "Prussian tribes" ugh.
Also, 20 years? So she's in her late 20ies or early 30ies. Realistically, women don't remain unmarried till this age in pre-industrial societies, such as this setting. Even now most have kids. But she's some kind of special fictional female warrior... so I can't criticize that part, right?