Ok I know this sounds a weird question, but is it posible for a women to fall pregante 5 years after her tubes were done?

My sister had her period last month but 3 weeks later bleed for 2 day not as a normal period and if goes by her normal date an normal last period of last month she is nearly 2 weeks over due for it, she tired alot an friend of hers told her she could be pregante? Is this posible?