A couple of things may have happened:
In addition to using your friend's referral link to purchase Ava Fertility, you also need to take note of the single-use discount code that appeared on your screen when you first opened her link and then manually type this code into the Discount box at checkout.
The referral program discount code only applies to Ava bracelet purchases. If you tried to purchase a strap or an accessory, unfortunately, this does not qualify for a referral discount.
Referrals only apply to referrers and referees residing in the same country. Unfortunately, these cannot be shared across different regions / currencies.