No, absolutely not, she is Actresses Rachael Leigh Cook you can Googled it.
Legally she is definitely can’t be his daughter because in 1994 Bill Gates got married to Melinda French Gates in a private ceremony held in Lanai, Hawaii. That time Melinda was also working in Microsoft and participated in the development of many of Microsoft’s multimedia products, later after the marriage she left the job to focus on starting and raising her family.
Later the couple bless with three children:- Jennifer Katharine Gates, his daughter born in 1996
- Rory John Gates, his son born in 1999
- Phoebe Adelle Gates, his daughter born in 2002
So as of now in 2010 Jennifer Katharine Gates age will be 14, and i don’t think the girl in picture look like 14 year old girl.