Looking for a Natural Mint Recipe or Concentrate that holds it flavour

I personally don’t vape Mint flavours. But my sister does and I have done a couple of different mixes for her including FlavorWest Candy Cane @ 15%, Atmos Lab Peppermint @ 6% Flavourart Peppermint @ 3% and Hic’s Tic Tac mix from the recipe on here.

All 3 have lost there flavour before she has finished the 50ml bottles I have made up for her after she liked the initial 10ml samples I made first.

She hates menthol so it will have to be proper natural mint or a peppermint type vape anyone got any suggestions for a good mint concentrate or recipe. So I can crack this for her.

I mix all AG for myself but have mixed hers at 70/30 VG/PG which should be ok for mint I would have thought?