Glad you went to the GP but she's a bit out of date on a couple of things. If you feel strongly- and after all it's your body and your life- I'd think about doing some research, printing stuff off and going back.
The NICE guidelines are very clear that HRT should be the treatment for women with menopause under 45 (some consultants raise this to 47.) The guidelines also say don't do blood tests on women under 45, not under 40. As you are 42 she ought to do blood tests.
This is from Menopause Matters ( person who writes this is chair of the British Menopause Society. www.menopausematters.co.uk/pm-definition.php
Premature Menopause: Definition
Premature menopause, or premature ovarian failure, is frequently defined as being menopause that occurs before the age of 40 years, but in the developed world, it is thought that it should be defined as menopause before the age of 45 years, the loss of estrogen having particular long term health risks in this age group.
If your periods do stop before 45 then HRT is recommended for both bones and prevention of heart disease. The jury is not out on it, as several studies show that HRT started within 10 years of the menopause protects against heart disease- it's called the 'window of opportunity'.
HRT is also available for women with low bone density. There are many consultants who would offer this to women under 60.
I think you have to see how you go and if your periods stop before 45, ask to be referred to a consultant for a 2nd opinion. If she won't agree, raid your savings and pay for the initial appt.