I have no direct experience, but I do know some people have dealt with this sort of situation by putting the new cat into a large dog crate in the main living area for part of the day, so she can feel safe from attack whilst the incumbent cat gets used to her presence
engaging both together with a wand toy like the Flying Frenzy is probably going to be the best way forward once they are safe to be together
given their respective ages, though, and this is from my own experience, older females often take naturally to the role of boss mother in a household, and it may take less time to integrate them or at least establish non-confrontational behaviour, by treating her as Number One Cat
they are a handsome pair, I must say, and I hope it works out - my older female has hissed and swiped at my younger boy for 9 years now, and he long ago learnt it was all bark and no bite
