2: Would she have been a slave?
Very unlikely in England at that time.
Wikipedia seems to indicate that internal slavery in Britain was unheard of by 1200.
I see no reason to doubt this. The feudal roles of serfs, cottars and others probably provided the invading Norman lords with all the control they wanted over their subjugated workforce.
The Atlantic slave trade started in the 16th century, first by the Portugese and later by the British and others. But that was not supplying slaves to work in Britain and initially the victims of the trade had the rights of indentured servants. I believe the victims were exclusively from Africa.
So there certainly wasn't any well established system capable of enslaving citizens of Japan and transporting them from Japan, or elsewhere, to Britain.
Were there slaves (and markets where one could publicly free them) in Great Britain in the mid-17th century?
A few slave owning people moving to Britain from America could have brought some slaves with them and continued to treat them as slaves. This status would almost certainly not have been supported in English or Scottish law.