In the Doctor's Daughter when Jenny "regenerated" why didn't her looks change like the Doctor's does?

I don't exactly know but I reckon it is because she is only half time lord.

The tenth Doctor also once regenerated without altering his appearance. Maybe it was the same as that.

She didn't regenerate. Her revival was caused Von The Source. She writes her father a letter telling him that and it can be found in this book.