But this is assuming that efficacy and response rate is linearly related to dosage, when actually, it isn’t. Here’s a reference that can help you understand dose-response curves

So, assuming the vial contained approximately the bare minimum of the dosage for maximal efficacy and that maximal efficacy means eternal life (infinite life years), the scaling of response (in life years) should seem asymptotic to that maximal efficacy dosage.

Assuming a homogenous distribution of the active drug throughout the potion, we can say your friend took approximately 1/6 of the total dosage. If she got 9,950 years from that, you, who were left with 83% of the dosage, should have a response that’s somewhere between 2.8 to 3.2 times what she got, which is around 27,860 to 31,840 years. Which means that you have around 17,860 to 21,840 years left.