I think this was a pretty good move by Tide to help promote their product. Not only is their product's name the same as Ms. White's but she is also ranked with Tom Hanks with the highest Q Score public favorability ranking. This could in turn boost the favorability of Tide Vivid White.
The objective for the addition of Betty White was more than likely to increase awareness and favorability of the product.
The target audience for this particular advertisement is for younger women, who are into fashion. Ms. White is encouraging users to break the rules and wear white. They shouldn't be afraid to get it dirty because Vivid White makes it much easier to clean.