I guess you could grant the equity on a standard vesting schedule with a 1-year cliff, but would your co-founder be comfortable firing her if it doesn't work out? You could also try more creative arrangements like performance-based equity tranche releases but I'd guess she'll find that insulting.

I personally wouldn't accept it, it dilutes your team's equity and opens up a huge can of worms around conflict resolution, and founder conflicts kill companies. I would think of this as-if your cofounder is asking for an additional 10% on his or her stake, because that's de facto what it's going to be. Your cofounder frankly also hardly knows this woman despite the fact that he or she rushed into marriage.