My friend's 4yo DS caught CP at Kindy (it isn't usually vaccinated against here, so it usually makes it's rounds) and generously passed it on to his 4 month old sister. They were both fine (although mum was shattered!). Another friend's both DDs caught it when the youngest was 10 months old. They were fine as well (although we chose to stop the donor milk from this friend in the meantime, to protect our DD, who was then 4 months old and very underweight).
Also, if shingles is as contagious as CP itself your mother has been contagious for several days before actually showing signs.