This is from the American Red Cross also, and the link...In addition, I have donated blood dozens of times while well under 150 pounds, and I'm 5'2"
Doing a quick search on that site for "150" one learns that requirement is for a person being a double red cell donor, which is a form of apherisis, meaning blood is cycled through you for a longer period, the red blood cells are collected, and the plasma and platlettes are returned to the bloodstream of the donor.
You might want to look about a dozen lines above where you are getting your information, to find the weight requirements for donating whole blood, which is by far the most common form of donation, and which is what the OPs friend can do to find her blood type for free, unless she weighs less that 110 pounds. It's all about blood volume.
You must weigh at least 110 lbs to be eligible for blood donation for your own safety. Students who donate at high school drives and donors 18 years of age or younger must also meet additional height and weight requirements for whole blood donation (applies to girls shorter than 5'6" and boys shorter than 5').
Blood volume is determined by body weight and height. Individuals with low blood volumes may not tolerate the removal of the required volume of blood given with whole blood donation. There is no upper weight limit as long as your weight is not higher than the weight limit of the donor bed/lounge you are using. You can discuss any upper weight limitations of beds and lounges with your local health historian.