We frequently leave a smaller piglet with mum after weaning the rest. You will see that her other teats dry up quite quickly leaving just the ones your piglets are using, and as the piglets grow they will naturally wean.
In nature,wild boar wean they young at about 16 weeks, and become quite forceful in ensuring tha weaners stop. Our mums tend to get stroppy with younsters at about 10-12 weeks, and we see little feeding after this.
So yes I would go ahead as you don't plan to mate her again for a while