Yeah I Think It was proberbly because she was dying, after all she died straight after giving you her power.
There's also the fact that the Dragon Slayer was apparently still very vulnerable after leaving Farglow and hadn't undergone the appropriate rituals yet that would stabilise her (except one that Rhode improvised on the spot).
Maybe that, too, would've made it easier for Talana to change you, especially since the young Dragon Slayer just had the whole of the Dragon Knight's ancestral memories or something dumped into her very being.
