My sister is 135lbs and shes 14 and 5'1, is this weight ok for her?

Probably a Bit High. There are average standards of ideal weight, which are only surveys, not scientifically based upon the "healthiest " weight.I think 110 to 120 pounds is reasonably appropriate based upon these standards.
Yes. If it seems right to her and she can keep up in gym class, it's good. The stuff about "ideal weights" is subscientific. I'm glad you care about your sister.