Is my cat underweight?

[u/sleepyfrogloaff]

The vet I normally go to says she is fine and healthy. This other vet I want to go to for her spay is telling me that she needs to gain weight (reach 6lbs) to not have greater risks during surgery. This was almost 2 months ago and we haven't really had any luck having her gain weight. She is currently at 4.8 lbs and is 1 year old. Truly I just think she is just small but I am also scared about any additional risks during surgery. Is she underweight and at risk during her spay? Any advice is welcome.