There is no maximum age limit for HRT - although it is not advised to
start it if you are more than 10 years post-menopause except under strict supervision (transdermal route preferred - though the skin), or over 60.
If her doctor is happy with it and she is well - then presumably that is OK? Do you know how long she has been taking it and what type?
I'm in my 60's and still taking it and there are several of us in this position on here - I don't think we have a 70 year old on HRT posting on here though - well not that she's admitting anyway
Hurdity x