As far as I know, in case of a strike there will be a complete embargo on all staff travel. Even if you already have tickets for use on another airline, BA will know if these were used. Your partner would then be in breach of staff travel policy, which could lead to disciplinary action. Loss of staff travel for a set period (around 2 years) would be the minimum punishment.
I'm happy to stand corrected if anyone else know more.
I'd recommend you get regular tickets, especially if you have somewhere you need to be at that time.
Gg