Britney Spears' mum has had a busy week of celebrations, with her 66th birthday on Tuesday and Cinco de Mayo on Wednesday.MORE: The Battle for Britney: Everything we know about Britney Spears' conservatorshipOn Thursday, the author posted a picture of herself posing with her granddaughter Ivey, as the pair wore some tiny sombreros and glasses decorated with sombreros.Ivey is the youngest daughter of Jamie Lynn Spears, who is in turn the youngest of Lynne's children.WATCH: Britney Spears wows in